I went to the NSA Cryptologic Museum back in 2002 while I was reading Cryptonomicon. Not only did they have Enigma machines, one exhibit had an Enigma out in the open that anyone could experiment with. The exhibits I was most impressed with were the Japanese encryption machines, Jade and Purple. These machines are quite rare and even the machines in these exhibits were incomplete.
SIGSALY was also interesting - I didn't know that voice encryption was possible during WWII.
I also found it amusing that they had a Connection Machines CM5. Sure, the CM 5's blinkin' lights are cool! But it was personally funny to me because my future brother-in-law used to work for Connection Machines and had a hand in their design and consturction. After I got home, I said to him, "Hey Sam, I saw some of your handy work in the NSA's museum".
The volunteers working at the museum were all retired NSA or military intelligence. These guys actually worked with some of the equipment on display and could expertly explain technical details.