I love going to ballparks when I travel, but the Cardinals have been out of town the last three times I was in St. Louis. I did eat at the village Gunnie mentioned, but that unfortunately doesn't count.
So far my stadium tour includes the following teams: Orioles, Nationals, Yankees, Mets, Pirates, Red Sox, Cubs, Rockies, Diamondbacks, Blue Jays, Phillies, Dodgers, Royals, and Brewers.
Oddly, I have never been to an American League West ballpark. I once stayed at the Marriott that overlooks the Padres stadium, but the season had yet to start when I was there.