Angel Stadium home of the
Los Angeles Angels of Anaheim

Angel Stadium of Anaheim (formerly Anaheim Stadium and Edison International Field of Anaheim) opened April 16, 1966 and has a seating capacity of 45,050.
More info about Angel Stadium.

Angel Stadium
I took this picture while I was at Angel Stadium in 1999 while attending the Barbershop Harmony Society International Competition. I can't find a picture with me in it and this was before I came up with the brilliant stadium t-shirt idea, so I don't have a t-shirt either. Ray will vouch for my actually being at the stadium though.
Me at The Big A in June 2016 (got a pic this time).
It's hard to see, but there is a blueprint of the stadium in the background of the shirt.

Minute Maid Park home of the
Houston Astros

Minute Maid Park (formerly known as The Ballpark at Union Station, Enron Field and Astros Field) opened April 7, 2000 and has a seating capacity of 40,950.
More info about Minute Maid Park.

Minute Maid Park
Dennis and I at Minute Maid Park. This stadium is GREAT! Also, we struck up a conversation with an usher while we were exploring the Club level and told her about my stadium quest and later when we went to our seats, she came down and brought us 2 free Astros hats. How cool! Also, the Astros won, ending a 12 game losing streak.
Minute Maid Shirt
Shirt from Minute Maid serves two purposes: 1) Stadium shirt 2) Mentions we were there in last season of them in the National League.

The Coliseum home of the
Oakland Athletics

The Oakland-Alameda County Coliseum (formerly known as Network Associates Coliseum and McAfee Coliseum) opened September 18,1966; the Athletics have played there since 1968. The Coliseum has a seating capacity for baseball of 35,067.
More info about The Coliseum.

I drove by The Coliseum once, but haven't been inside it...It's the only California stadium I haven't made it to...

Safeco Field home of the
Seattle Mariners

Safeco Field opened July 15, 1999 and has a seating capacity for baseball of 47,116.
More info about Safeco Field.

Closest I have been was Portland, OR

Rangers Ballpark home of the
Texas Rangers

Rangers Ballpark in Arlington (formerly The Ballpark in Arlington and Ameriquest Field in Arlington) opened April 1, 1994 and has a seating capacity of 49,170.
More info about Rangers Ballpark.

Rangers Ballpark
Dennis and I at Rangers Ballpark, July 2012. The White Sox beat the Rangers 9-5. Chris Sale v Yu Darvish. Youk and Alexei homered.
Rangers Ballpark Shirt
They actually had several shirts that at least mentioned the stadium. They had 2 that were specifically stadium Ts and this one was significantly better than the other which was like the Toronto and Detroit ones.
American League East
Camden Yards - Baltimore
Fenway Park - Boston
Yankee Stadium - New York
Tropicana Field - Tampa Bay
Rogers Centre - Toronto
American League Central
US Cellular Field - Chicago
Progressive Field - Cleveland
Comerica Park - Detroit
Kauffman Stadium - Kansas City
Target Field- Minnesota
American League West
Angel Stadium - Anaheim
Minute Maid Park - Houston
The Coliseum - Oakland
Safeco Field - Seattle
Rangers Ballpark - Texas
National League East
Turner Field - Atlanta
Marlins Park - Miami
Citi Field - New York
Citizens Bank Park - Philadelphia
Nationals Park - Washington
National League Central
Wrigley Field - Chicago
Great American Ballpark - Cincinnati
Miller Park - Milwaukee
PNC Park - Pittsburgh
Busch Stadium - St. Louis
National League West
Chase Field - Arizona
Coors Field - Colorado
Dodger Stadium - Los Angeles
Petco Park - San Diego
AT&T Park - San Francisco
Other Ballparks
Comiskey Park - Chicago
Olympic Stadium - Montreal
Old Busch Stadium - St. Louis