Washington, DC
SEVERAL convention centers and other possible venues. It's the capitol. Not at some uber-commercialized theme park. Not TOO expensive to get to. Close to two of the largest regionals (Richmond and Annapolis). Oh yeah, my team would have ZERO travel cost :-)
Seriously, why isn't there AT LEAST a regional there! It seems obvious...
I SWEAR that if a FIRST event comes to DC, my entire team will walk there, transporting everything on a dolly. Oh, and I'll eat a FIRST hat. While walking. Backwards.
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Someone mentioned tight security? I live within biking distance of the mall (about 20-30 mins) and security isn't THAT tight. If someone forgot to empty their pockets of tools, they'd probably only get it confiscated. Well, as long as you don't LOOK like a terrorist

(A friend of mine, who is egyptian, always grumbles about constant "security issues")