I'd love to get in on this one - I go to ball games whenever possible while travelling.

My votes, in order, would be

BOS
NY (AL)
CHI (NL)
BAL
DET
SF
SEA
HOU
and of course CLE (been there 20+ times, but I'll always go back)

Hey Tribeflyer - in the last 2 years I've managed to catch the Tribe in CLE, KC, OAK, ANA, TEX, HOU, SEA, DET, and just missed TB this year.