Replying to Road Trip stops

A few of my friends and I are planning to take a HUGE road trip around the US next summer (as in, the circumference of the lower 48).  We're starting in Pensacola, FL, and some of our major stops are going to be Austin, the Grand Canyon, Las Vegas, Los Angeles, San Francisco, Seattle, Mt. Rushmore, Chicago, Niagara Falls, Boston, New York, DC, and down to Key West.  We're thinking 3-4 weeks.  Anyway, I'm looking for interesting/fun/weird places to stop between cities.  Pretty much anything from a great local dive to the World's Second-Biggest Ball of Twine is fair game for us.