Baltimore does have the 1st Mariner Arena, a decently sized place for a big event --- maybe not big enough for a Political Convention though.
If they need the convention to hold Maryland, they're toast anyway. While Baltimore would be better than Boston, it doesn't have enough "Southerness" to make an impact outside of a state that Kerry should be ignoring.
I'll take your word on it Angus, I haven't traveled as much.
That leaves:
Good places for the Dems:
New Orleans
Philadeplhia
Cleveland
Milwaukee
Miami
Good places for the Reps:
Pittsburg
Cleveland
Milwaukee