Camden
RFK
Nats Park
PG Stadium
Space Coast
Rangers Ballpark in Arlington
Dolphins Stadium
Great American Ballpark
Nats Park and RIBA my favorites. PG was cool as a kid, because players were so accessible. Haven't been in 10+ years though, so I'm not sure how it is now. Got a cracked bat there haha.
Nats Park: as said, love the angles.
RIBA: Great ballpark. Now that the Rangers are a hot ticket, it's 'fun factor' has gone down. Bit too expensive now, for me.