If you haven't been, and you're in the bay area, you really should go here. Sure, the nostalgia is wonderful, but they take their work seriously. Last time I went I was talking with one of the docents about an effort they were taking to get the original Unix v1.0 source collected and compiling.
Yes, yes, yes. This is a wonderful place. I visited it when it was just a shack on Moffett Field and now it's in the old SGI building.
If you are in the UK and can't make it to CA then a substitute is the National Museum of Computing: http://tnmoc.org/ It doesn't have the depth of the collection seen in Mountain View, but it does have some wonderful pieces. And the staff worked on the machines that are on display. Got the opportunity to show my SO core memory the other day.
Somewhat related, though the exhibits aren't as nice- The National Cryptologic Museum in Maryland. If nothing else, it's an excuse to venture on to the grounds at Ft. Meade.
When I visited a number of years back, there was a guy selling cell phones on a little folding table outside the front door. Which seemed...odd...for any number of reasons, given the location.
Seconded. The docents are, IMO, the most amazing thing about the museum. Incredibly knowledgeable, many of them were involved in making the machines on display. It's a truly wonderful place made more wonderful by the people who are involved.
As someone who visits the Bay Area and doesn't have a car, how can I reach that museum via public transit? BART doesn't reach that far down in the west bay.
Google Maps also includes a transit trip planner; enter endpoints as if driving then toggle to the railcar icon (among the car, railcar, walk, bike icons). From SFO to the Computer History Museum it suggests routes using a combination of BART, CalTrain, and VTA bus.
I haven't been to the Computer History Museum (it's been years since I've been in the Bay area), but I did stop by the American Computer Museum in Bozeman, Montana once on a cross-country drive. For something literally stumbled across in a tour guide I was honestly impressed with the collection. It's worth a look if anyone is ever in the area.