Not sure if anyone has mentioned these three:
Hiller Museum at San Carlos Airport just south of San Francisco is quite nice if you are in the area - also there's a small museum at Oakland Airport which has a Short Solent amongst its exhibits.
Helicopter Museum at Brandywine in Pennsylvania - lots of interesting airframes, we happened to do a touch and go in a C172, noticed an early V-22 outside and went round for a full stop and a tour. Again, worth it if you are in the vicinity.
Finally, Old Rhinebeck up the Hudson from NYC - lots of interesting old aircraft and if you can do a show, they are fun...