Starting off the 2014 season I have seen a professional level game at 87 different parks:

• 16 currently active MLB parks
• 6 former MLB parks
• 19 Spring Training facilities (when used for a ST game)
• 9 AAA
• 6 AA
• 19 A
• 12 Independent 

I specify professional level games as two parks I've been to have been for the WBC (PetCo and AT&T).

I've seen games in 24 different states plus DC.  (I have yet to see a game outside the US, though that is a goal).

For the 2014 season I plan to add 7 new parks - five of them on one trip to Chicago in August:

• US Cellular
• Stanley Coveleski Regional Stadium (South Bend, IN)
• Aviators Stadium (Loves Park, IL)
• Silver Cross Field (Joliet, IL)
• Standard Bank Stadium, (Crestwood, IL)