AL East AL Central AL West  
BAL: Camden Yards
BOS: Fenway Park
NYY: Yankee Stadium / New Y.S.
TAM: Tropicana Field
TOR: Skydome
CHW: New Comiskey Park
CLE: Jacobs Field
DET: Comerica Park
KAN: Kauffman Stadium
MIN: Metrodome / Target Field
ANA: Angel Stadium
OAK: Network Assoc. Coliseum
SEA: Safeco Field
TEX: Rangers Ballpark in Arlington
NL East NL Central NL West
ATL: Turner Field
MIA: Miami Marlins
(MON: Olympic Stadium)
NYM: Shea Stadium / Citi Field
PHI: Veterans / Citizens Bank
WAS: Nationals Park
CHC: Wrigley Field
CIN: Great American Ball Park
HOU: Minute Maid Park
MIL: Miller Park
STL: Busch Stadium / Busch II
ARI: Chase Field
COL: Coors Field
LA: Dodger Stadium
SF: SBC Park

PNC Park, Pittsburgh, PA. August 9, 2002

Current tally (May 2016):

27 parks visited, the homes of 26 teams (old and new Yankee Stadium)

9 parks left to visit...

...4 of which are new to teams whose old parks I've already visited (Twins, Phillies, Mets, Cardinals)...

...and 5 which belong to teams whose parks I haven't visited, which would make a nice Southern road trip (Diamondbacks, Astros, Rangers, Braves, Rays)

Also, 1 park I visited whose team is no longer in existence (Expos)