I was planning to do something like that in the summer of 2008. Since I'll be flyin' in from Europe, I've still not decided whether or not it is better to purchase some cheap (low consumption) vehicle or purchase a 30 days Rail Pass.
The idea was to fly in to Washington DC., do some sightseeing and head out for New Haven where I have arranged accommodation in my friends house. Some time will be spent there, mostly to check out New York and the surrounding area. From there we would go to Boston, Massachusetts and visit MIT and Harvard where we will hopefully be able to sleep over. Then on, we head out for Chicago, but on the way visit Cornell university and again sleep over in the dorms. Since Niagara Falls aren't that distant we might just make a detour and visit them as well. If we do, then Toronto will be way to close not to visit, so... you guess, we go cross border to Canada. Continuing our way to Chicago we pass through Detroit, visit Michigan university (again to sleep over) and finally arrive in Chicago.
Once we've seen enough of Chicago we head for University of Illinois at Urbana Champaign, sleep over, and continue our way to Kansas via St.Louis. In Kansas we have another friend, so some time will be spent exploring the geography. Then we go to Colorado, probably visiting Colorado Springs, and continue to Utah into Salt Lake City. A visit to Utah university is a must, since I'll probably be enrolling there for graduate study and we have some friends that already are there. Oh, and I'll be converting to Mormonism there
Next stop is Las Vegas, Nevada and our final destination: California. The plan was to go to San Francisco and visit Berkeley university, where yet again we have a friend studying there, and crash in his room. Last two stops are Irvine university and Stanford university. We spend a day or two in LA and fly back to Europe.