RAF Museum, London, UK
RNthAF museum, Kamp Zeist (Soesterberg AB), the Netherlands
Twente AB museum, Twente AB, the Netherlands (small, private run, well worth it if you can find it
US Navy museum, Pensacola, USA
USMC Museum, Quantico, USA
Castle Air museum, Castle AFB, USA
Smithsonian A&S museum, Washington DC, USA
All different, all fun. US seems to concentrate more on the aircraft themselves, and Europe more on the history surrounding them.