Angela, I am not a kid anymore but I sure got a thrill from standing in four states at once! That has been on my list of "things to do before I die" for a long time and I'm glad I was able to do it.
Haven't been as well-traveled around the US as I would like, but of what I've seen, I'd say:
Bryce Canyon N.P.
San Antonio missions
Texas Hill Country
Washington D.C. monuments
Florida Keys and Key West
St. Augustine, FL
Smokey Mountains and Blue Ridge Parkway