Some of the best and fun spots to go for summer vacation in the US include: Grand Canyon, Yosemite National Park, Mendenhall Glacier, Ossipee River, Maine as well as Colorado. These areas have quite a number of amazing beaches and amusement parks which offer great experience.
I like Virginia. It has something for everyone. You have the beach in the east, mountains in the west, and a lot of culture and history in between. If you stay centrally in Richmond nothing is more than 90 minutes away. Including Washington DC.
Depends on what you're looking for. If you want a busy city, I recommend Boston. Teeming with historical stuff to see, cool stuff to do, and some of the friendliest people I've ever met (no, I don't live there, and I never have!). If you want a really quiet, relaxed kind of vacation, one of my best was in Silver City, New Mexico - long walks through the pines, a tiny town with lots of artsy-craftsy shops and stuff to look at. Not a great deal to do, but if you like to make your own entertainment, this place is tops.