I'll have to say New York.... I planned a trip there a long time ago, but it never got off the planning stage
I've been to San Francisco and Oklahoma, both fantastic places, nicely different from each other.
New York has a sort of mystique for me, I guess... It's essentially all the fictional comic cities in one- it's Gotham, Metropolis and all the rest, plus visiting DC's offices and Marvel's would be cool...
I quite liked America when I was there. Sure, there's plenty to not like, but no more so than any other country I've been to, plus I haven't left my own in bloody aaaaages...
There are too many things I want to see/do in New York, really, but at the same time, I've got to admit to just wanting to see it, warts and all, and see if it's as frightening and awesome as my received perceptions and stories from friends have made it out to be.