Europe is always a great option. My advice would be try to go either really early, or really late in the summer. Some of the best cities get terribly overcrowded during the tourist season. There's also places close to home that might be of interest. If you wanted to save a little money you could look at Charleston SC hotels, Cape Cod Hotels, Marthas Vineyard Hotels, or even some place you'd never think of like Sante Fe, NM.
I've heard Cape Cod and Marthas Vineyard are gorgeous, but only during the summer. It gets pretty cold there once the seasons turn. The woods hole ferry sounds like a fun way to get there too. I like ferries too. It's a nice reminder that you're going some place different.