Both Yankee Stadiums, Citi/Shea multiple times for the Mets and one trip to Wrigley when I was visiting a friend in Chicago. My most memorable moment in each stadium:
Old Yankee Stadium: My first game there in '05 where Pedro got the win and the Mets held on late despite Braden Looper starting a dumpster fire in the ninth nearly blowing a 6-2 lead. Think I was only there twice...the other game the Mets trailed 11-6 and rallied off Rivera in the ninth to make it 11-8 and load the bases before Beltran swings at the first pitch and pops up capping an 0-5 day for him
New Yankee Stadium: The Luis Castillo dropped pop-up game <shudder> (and that was the first sports event I'd been to since the haunting Game 7 loss to the Hurricanes several weeks before that)
Shea Stadium: Mets clinch the NL East in '06
Citi Field: The tears of joy Flores extra-inning walkoff against the Nats post-trade deadline last year
Wrigley Field: Carlos Zambrano jacking a three-run HR. It was a Cubs-Cardinals game that the Cubs won like 7-3. I think Pujols did have a HR too.
I've only been to a couple of minor league stadiums - whatever the stadium in Brooklyn's called now for the Mets' single A team and I went to Augusta to see a minor league game when the Cardinals had their single A team there.
So nobody has done the 30 stadiums in 30 days trip? I've always wanted to accomplish that, I just don't have the time to do it. Everyone I know who has done it is either retired or owns their own company.
Fenway and Dodger Stadium I really want to go to...pretty much everything else I can take or leave.