I've been to a lot of avaition muesums. Most of my favorites have already been named: NASM, Wright Patterson AFB, Naval Air Museum, etc.
However, when you can, check out the smaller ones, you'd be surprised at what you can find.
We were driving on I-10 back from Florida to Texas, when we decided to stop at the USS Alabama battleship muesum. Surprise! It has a small air muesum as well. They had a VERY nice looking F4U they had recently restored. But, they also had one of the very rare SR-71 2 seater models. And an extremely rare (only 2 ever built) YF-17 Cobra. For those who don't know, it competed against the F-16 for the Lightweight Fighter contract. Though it didn't win, Northrop and McD teamed up and used the YF-17 as the baseline for the F-18.
Many years ago, I did the last airshow at Castle AFB, CA before the base was shut down. I happened to stop by their outdoor air muesum, and they had, wonders of wonder, a Northrop (?) A-9! The A-9 competed against the A-10 for that contract but lost. I think only 2 were ever built as well. It's an interesting looking aircraft, kind of like a supersized T-37. Makes you wonder where the Russians got their inspiration for the Su-25 Frogfoot. I hope someone (maybe even the USAF) will have picked it up and restored it to display somewhere inside.
Fly Safe!
FastCargo