Last week I was in Dayton, Ohio for work and was able to take in the National Museum of the U.S. Air Force.  It was great, it was free and it was huge.  Anyone with any thought of going. should.  With it being free you can't beat the price and make sure you have plenty of time.  Three hours or so.  There are four large hangers filled with airplanes, many of which I've never seen before.  They don't skimp.  No matter how large or how small it seems like you'll find it here either in a ground display or hanging from the rafters.  There are also other displays as well as a nice gift shop.  This isn't something they just threw together. The facilities are very nice and I found it nothing short of fun.  The pictures below are just a small sample of what I took and much smaller sample of the total displays.