I compiled the below info from www.baseball-reference.com, which lists all trades that have occurred during the Billy Beane Era. My main take-away: when the A's win on a deal, they win big; when they lose, they lose by a lesser margin.

The wins:

7/31/99: Traded Billy Taylor for Jason Isringhausen

12/7/00: Traded Miguel Olivo for Chad Bradford

1/8/01: Traded Ben Grieve and Angel Berroa for Johnny Damon, Mark Ellis, & Cory Lidle.

7/26/01: Traded Mario Encarnacion, Jose Ortiz, and Todd Belitz for Jermaine Dye.

12/7/01: Traded Eric Hinske and Tyler Yates for Billy Koch

3/19/02: Traded Luis Vizcaino for Justin Duchscherer 12/3/02: Traded Billy Koch for Keith Foulke

12/18/04: Traded Mark Mulder for Dan Haren, Daric Barton, and Kiko Calero

The losses:

7/23/99: Traded Kenny Rogers for Terence Long

1/14/02: Traded Ryan Ludwick and Gerald Laird for Carlos Pena

7/5/02: Traded Carlos Pena and Jeremy Bonderman for Ted Lilly

7/30/03: Traded Aaron Harang for Jose Guillen

11/18/03: Traded Ted Lilly for Bobby Kielty

6/24/04: Traded Mark Teahen for Octavio Dotel

12/16/04: Traded Tim Hudson for Dan Meyer, Juan Cruz, and Charles Thomas

7/13/05: Traded Eric Byrnes and Omar Quintanilla for Joe Kennedy and Jay Witasick

The complete list:

11/7/97 Traded a player to be named later to the New York Yankees. Received Kenny Rogers and cash. The Oakland Athletics sent Scott Brosius (November 18, 1997) to the New York Yankees to complete the trade.
11/26/97 Traded David Newhan and Don Wengert to the San Diego Padres. Received Doug Bochtler and Jorge Velandia.
12/8/97 Traded Steve Karsay to the Cleveland Indians. Received Mike Fetters.
12/19/97 Traded Eric Ludwick to the Florida Marlins. Received Kurt Abbott.
6/9/98 Traded Kurt Abbott to the Colorado Rockies. Received a player to be named later and cash. The Colorado Rockies sent Ara Petrosian (minors) (June 18, 1998) to the Oakland Athletics to complete the trade.
6/23/98 Traded a player to be named later to the Detroit Tigers. Received Bip Roberts. The Oakland Athletics sent Jason Wood (July 18, 1998) to the Detroit Tigers to complete the trade.
7/12/98 Traded a player to be named later to the Cleveland Indians. Received Tim Worrell. The Oakland Athletics sent Adam Robinson (minors) (July 28, 1998) to the Cleveland Indians to complete the trade.
7/31/98 Traded Scott Rivette (minors) to the Toronto Blue Jays. Received Ed Sprague.
12/8/98 Traded a player to be named later and Shane Mack to the Kansas City Royals. Received Mike Macfarlane. The Oakland Athletics sent Greg Hansell (May 9, 1998) to the Kansas City Royals to complete the trade.
3/30/99 Traded Jay Witasick to the Kansas City Royals. Received a player to be named later and cash. The Kansas City Royals sent Scott Chiasson (June 10, 1999) to the Oakland Athletics to complete the trade.
7/23/99 Traded Kenny Rogers to the New York Mets. Received Terrence Long and Leo Vasquez (minors).
7/29/99 Traded Jeff Davanon, Nathan Haynes, and Elvin Nina (minors) to the Anaheim Angels. Received Omar Olivares and Randy Velarde.
7/31/99 Traded Jeff D'Amico, Brad Rigby, and Blake Stein to the Kansas City Royals. Received Kevin Appier.
Traded Billy Taylor to the New York Mets. Received Jason Isringhausen and Greg McMichael.
8/18/99 Traded a player to be named later to the Milwaukee Brewers. Received Rich Becker. The Oakland Athletics sent Carl Dale (August 20, 1999) to the Milwaukee Brewers to complete the trade.
12/13/99 As part of a 3-team trade, traded Jimmy Haynes to the Milwaukee Brewers. Received Justin Miller from the Colorado Rockies and cash from the Milwaukee Brewers. In addition, the Colorado Rockies sent Henry Blanco and Jamey Wright to the Milwaukee Brewers and the Milwaukee Brewers sent Jeff Cirillo and Scott Karl to the Colorado Rockies.
2/18/00 Traded Brett Laxton to the Kansas City Royals. Received Jeremy Giambi.
7/28/00 Traded Jesus Colome to the Tampa Bay Devil Rays. Received Todd Belitz and Jim Mecir.
7/31/00 Traded Danny Ardoin to the Minnesota Twins. Received Mario Valdez.
8/30/00 Traded Jorge Velandia to the New York Mets. Received Nelson Cruz.
11/17/00 Traded Randy Velarde to the Texas Rangers. Received Aaron Harang and Ryan Cullen (minors).
11/20/00 Traded Matt Stairs to the Chicago Cubs. Received Eric Ireland (minors).
12/7/00 Traded a player to be named later to the Chicago White Sox. Received Chad Bradford. The Oakland Athletics sent Miguel Olivo (December 13, 2000) to the Chicago White Sox to complete the trade.
1/8/01 As part of a 3-team trade, traded Ben Grieve to the Tampa Bay Devil Rays and Angel Berroa and A.J. Hinch to the Kansas City Royals. Received Cory Lidle from the Tampa Bay Devil Rays and Johnny Damon and Mark Ellis from the Kansas City Royals. In addition, the Tampa Bay Devil Rays sent Roberto Hernandez to the Kansas City Royals.
3/28/01  Eric Hinske acquired from the Chicago Cubs for Miguel Cairo and A''s refuse the return of Rule 5 selection Scott Chiasson; Omar Olivares traded to Pittsburgh for a player to be named later or cash.
6/19/01 Traded Ryan Christenson to the Arizona Diamondbacks. Received Rob Ryan.
7/3/01 Traded Robin Jennings to the Colorado Rockies. Received Ron Gant.
7/26/01  Acquired outfielder Jermaine Dye from the Kansas City Royals and sent outfielder Mario Encarnacion, infielder Jose Ortiz and pitcher Todd Belitz to the Colorado Rockies in a three-team trade
9/4/01 Traded Michael Wenner (minors) to the Chicago Cubs. Received Mike Fyhrie.
11/2/01 Traded Mark Bellhorn to the Chicago Cubs. Received Adam Morrissey (minors).
12/14/01  Acquired OF David Justice and cash from the New York Mets for P Mark Guthrie and minor league P Tyler Yates.
12/7/01  Acquired P Billy Koch from Toronto for minor league P Justin Miller and minor league 3B Eric Hinske.
1/2/02  traded C Tom Wilson to the Toronto Blue Jays for minor league C Mike Kremblas;
1/14/02  Acquired LHP Mike Venafro and 1B Carlos Pena from the Texas Rangers in exchange for LHP Mario Ramos, OF Ryan Ludwick, 1B Jason Hart and C Gerald Laird.
3/19/02  Traded pitcher Luis Vizcaino to the Texas Rangers for pitcher Justin Ducchscherer.
5/22/02   Traded outfielder Jeremy Giambi to the Philadelphia Phillies for infielder-outfielder John Mabry
7/5/02 As part of a 3-team trade, traded a player to be named later, Carlos Pena, and Franklyn German to the Detroit Tigers. Received Ted Lilly, John-Ford Griffin, and Jason Arnold (minors) from the New York Yankees and cash from the Detroit Tigers. In addition, the Detroit Tigers sent Jeff Weaver to the New York Yankees. The Oakland Athletics sent Jeremy Bonderman (August 22, 2002) to the Detroit Tigers to complete the trade.
7/31/02  Acquired pitcher Ricardo Rincon from the Cleveland Indians for infielder Marshall McDougal; designated pitcher Mike Magnante for assignment.
7/26/02  Acquired second baseman Ray Durham from the Chicago White Sox for pitcher Jon Adkins.
8/22/02  Sent right-handed pitcher Jeremy Bonderman to the Detroit Tigers as the player to be named later in the July 5 trade with Detroit and New York.
11/16/02 Traded Cory Lidle to the Toronto Blue Jays. Received Mike Rouse and Christopher Mowday (minors).
12/3/02 Traded players to be named later and Billy Koch to the Chicago White Sox. Received Keith Foulke, Mark L. Johnson, Joe Valentine, and cash. The Oakland Athletics sent Neal Cotts (December 16, 2002) and Daylon Holt (minors) (December 16, 2002) to the Chicago White Sox to complete the trade.
12/15/02 As part of a 4-team trade, traded a player to be named later to the Toronto Blue Jays. Received Erubiel Durazo from the Arizona Diamondbacks. In addition, the Toronto Blue Jays sent Felipe Lopez to the Cincinnati Reds and the Cincinnati Reds sent Elmer Dessens and cash to the Arizona Diamondbacks. The Oakland Athletics sent Jason Arnold (minors) (December 16, 2002) to the Toronto Blue Jays to complete the trade.
12/16/02 Traded Jose Flores to the San Diego Padres. Received Buddy Hernandez (minors).
1/27/03 Traded John-Ford Griffin to the Toronto Blue Jays. Received a player to be named later. The Toronto Blue Jays sent Jason Perry (minors) (June 23, 2003) to the Oakland Athletics to complete the trade.
7/30/03  Acquired OF Jose Guillen from the Reds for minor league P Aaron Harang, P Joe Valentine and P Jeffrey Bruksch.
11/26/03  Acquired OF Mark Kotsay from the Padres for C Ramon Hernandez and OF Terrence Long.
11/18/03  Acquired outfielder Bobby Kielty and a player to be named later or cash from Toronto for left-handed pitcher Ted Lilly.
12/18/03  Chris Hammond: Acquired LHP Chris Hammond and cash from the Yankees for RHP Eduardo Sierra and nonroster INF J.T. Stotts.
12/17/03  Acquired LHP Mark Redman from the Marlins for RHP Mike Neu and a player to be named or cash.
12/15/03 Traded Michael Barrett to the Chicago Cubs. Received Damian Miller and cash.
Traded a player to be named later to the Montreal Expos. Received Michael Barrett. The Oakland Athletics sent Bret Price (minors) (December 19, 2003) to the Montreal Expos to complete the trade.
4/17/04 Traded Chad Harville to the Houston Astros. Received Kirk Saarloos.
6/24/04  Acquired RHP Octavio Dotel and cash from the Kansas City Royals in exchange RHP Mike Wood and 3B Mark Teahen. The Royals acquired Dotel from the Houston Astros along with C Jon Buck in exchange for OF Carlos Beltran.
11/27/04  Acquired C Jason Kendall and cash considerations from Pittsburgh in exchange for LHPs Mark Redman and Arthur Rhodes and cash considerations.
12/18/04  Acquired RHPs Dan Haren and Kiko Calero and C Daric Barton from St. Louis for LHP Mark Mulder.
12/16/04  Acquired LHP Dan Meyer, RHP Juan Cruz and OF Charles Thomas from Atlanta for RHP Tim Hudson.
12/15/04  Acquired IF Keith Ginter from the Milwaukee Brewers in exchange for RHP Justin Lehr and OF Nelson Cruz.
5/15/05  Acquired nonroster RHP Ryan Glynn from the Blue Jays for cash.
7/13/05  Acquired LHP Joe Kennedy and RHP Jay Witasick from the Colorado Rockies for OF Eric Byrnes and INF Omar Quintanilla.
   Acquired OF Jay Payton and cash considerations from the Boston Red Sox in exchange for RHP Chad Bradford.
12/13/05  Acquired OF Milton Bradley and INF Antonio Perez from the Los Angeles Dodgers in exchange for OF Andre Ethier.
12/5/05  Acquired RHP Chad Gaudin from the Toronto Blue Jays in exchange for a player to be named later; Designated C John Baker for assignment.
12/8/05  Sent Minor League OF Dustin Majewski to the Toronto Blue Jays as the player to be named later in the Dec. 5 trade where RHP Chad Gaudin was acquired.
3/31/06  Acquired RHP Juan Dominguez from the Texas Rangers in exchange for IF/OF Freddie Bynum and LHP John Rheinecker.
3/26/06 Acquired LHP Brad Halsey from the Diamondbacks for RHP Juan Cruz.
4/4/06  Acquired RHP Kazuhito Tadano from the Indians in exchange for OF Ramon Alvarado and optioned him to Triple-A Sacramento.
11/28/06  Acquired INF Donnie Murphy from the Kansas City Royals in exchange for cash considerations.
1/23/07  Acquired RHP David Shafer and PTBN from the Cincinnati Reds in exchange for RHP Kirk Saarloos and PTBN.
3/30/07  Traded C John Baker to the Marlins for 1B Jason Stokes and signed INF Todd Walker to a Minor League contract.
4/29/07  Acquired OF Ryan Langerhans from the Atlanta Braves for a player to be named later or cash;
4/28/07  Sent RHP Marcus McBeth to the Cincinnati Reds.
4/27/07  Acquired OF Chris Denorfia from the Cincinnati Reds in exchange for two players to be named later and cash considerations.
5/3/07  Acquired OF Jack Cust from the San Diego Padres for a player to be named later or cash considerations.
5/2/07  Acquired OF Chris Snelling from the Washington Nationals in exchange for OF Ryan Langerhans.
5/30/07  Acquired OF Dee Brown from the Arizona Diamondbacks in exchange for cash considerations.
5/4/07  Acquired nonroster catcher JD Closser from the Brewers for nonroster outfielder Charles Thomas.
6/9/07  Traded C Adam Melhuse to Texas for cash considerations
6/26/07  Acquired nonroster RHP Jermaine Van Buren from the Nationals for a player to be named later.
6/29/07  Traded OF Milton Bradley and cash to the San Diego Padres for RHP Andrew Brown
7/13/07  Acquired RHP Julio Manon from the Cincinnati Reds in exchange for RHP Daniel Denham.
7/16/07  Acquired C Rob Bowen and LHP Jerry Blevins from the Chicago Cubs in exchange for C Jason Kendall and cash considerations
8/14/07  Acquired nonroster IF Jack Hannahan from the Detroit Tigers in exchange for nonroster OF Jason Perry
11/18/07  Traded INF Marco Scutaro to Toronto for Minor League RHP Kristian Bell and RHP Graham Godfrey.
12/14/07  Traded RHPs Dan Haren and Connor Robertson to the Arizona Diamondbacks in exchange for LHPs Brett Anderson, Dana Eveland and Greg Smith, INF Chris Carter and OFs Aaron Cunningham and Carlos Gonzalez.
1/14/08  Acquired RHP Joey Devine, nonroster RHP Jamie Richmond and cash from the Braves for OF Mark Kotsay.
1/3/08  Traded OF Nick Swisher to the Chicago White Sox for LHP Gio Gonzalez, RHP Fautino De Los Santos and OF Ryan Sweeney.
6/5/08  Traded INF Kevin Melillo to the Blue Jays for cash considerations.
7/8/08  Sent RHPs Rich Harden and Chad Gaudin to the Chicago Cubs for RHP Sean Gallagher, C Josh Donaldson, INF Eric Patterson and OF Matt Murton