If you're interested in historical stuff there's plenty of stuff to do in most of the major East Coast cities (colonial era, civil war, etc.). Washington, DC comes to mind of course. Charleston (Fort Sumter, et al) and most of the rest of the Carolina coast has a lot if interesting stuff to offer. Depending on how far inland you're planning on going, I hear Philadelphia has some good spots (never been myself).
I enjoyed Washington, DC and Charleston, South Carolina very much. Washington for the history and museums.
Of course there's always New York. I've never been but I'd love to go, if only to see/hear the New York Philharmonic.