Over the last few years I have been a regular visitor to our own British equivalent, Bletchley Park, which is both a cryptography museum and also houses a historical collection of computers. If you’re in the UK, or visiting (Bletchley is about an hour North of London), then I would highly recommend a visit. Bletchley Park is an estate with a victorian manor house, and during World War II it was the scene of operations of the UK’s codebreakers, including computer pioneer Alan Turing.
It sounds like Bletchley and the NSA’s museum have many things in common, both exhibiting the (in)famous German Enigma coding machine, and both having Cray supercomputers on display. I will certainly put the National Cryptologic Museum on my list of places to visit the next time I’m in the Washington area.