We didn't take a tour when we went, but it was still fun. There are several large aircraft in the Presidential hanger. A VC-137 (tail number 26000) is the highlight, but there's 3 other piston aircraft too. FDR's DC-4, a DC-6, and a Connie are all available to walk though. I can't remember which one is the Sacred Cow, the Columbine's I and II, the Independence, etc. There are also some smaller planes like Nixon's Lockheed Jetstar. My dad wished that there was a hole in the plastic walls so that he could get some good photographs of the cockpits, but no such luck. My favorite aircraft were the B-1A, XB-70, and Douglas C-124 (I think).
There is one very important thing to remember when you go. The interiors of these airplanes are very narrow. They have plastic walls to protect the interior and you have to walk through a 17 inch wide thing before you can board. Being quarterback sized 16 year old, I had to turn on my side a couple of times because my shoulders were too wide. If you're thinking about a diet, starting one a couple months before you go would be a good idea. Incidentally, 17 inches is the width of the seats on Delta's 737-800s. Not very wide in my opinion.