I second going to Yosemite (the Sierras in general), Grand Canyon, Monterey or Carmel for exquisite natural beauty.
San Diego and that area would be nice to visit as well, they have a LOT to see.
San Francisco is interesting as well.
Perhaps one of the arranged tours would be easiest. We went on one through the kids' school, last May, to Washington, D.C. I'd never traveled with a tour group, but found it was wonderfully liberating not to have to hassle the driving, parking, directions, etc. Just let them drive and figure all that out!
I live in Southeastern CA, halfway between LA and Palm Springs, so my recommendations are based on what I'm famliar with. I can be at any of the following places in an hour (give or take, depending on traffic), and I love them all: desert (Joshua Tree, Palm Springs, Palm Desert), mountains (snow, lake, craggy mts, even a little zoo), big city (LA, cities in Orange County --- well, maybe I really don't love LA or the big city, lol), beach (Laguna, Newport Beach, etc). If I want to drive a little longer, I'm at San Diego in two hours. Or, Santa Barbara area is LOVELY!!
I did enjoy seeing the Washington DC sights, and we went to Williamsburg and Gettysburg and Annapolis as well. I'd like to see Boston someday, and Maine, and yes, New England. Was in San Antonio for some meetings about 5 yr ago, took a great bus tour of several missions (love historical sites). I hear Idaho and Colorado and Montana are stunning.
Gosh, I guess it all depends on what you WANT to see. If you like big cities' hustle and bustle, or historical sites (we have some ghost towns in CA), the amazing wonders of nature, that will decide where you'd most like to go/what you'd like to see.
Good luck deciding!