The Turing Bombe
Ever since I read Neal Stephenson's Cryptonomicon I've been fascinated by the early computers built during World War 2 to break the German and Japanese codes, so it was with some interest I saw that they have rebuilt a Turing Bombe at Bletchley Park. There's a Telegraph article and a news item at the museum's website.
Another really cool museum to visit some time. I should make a list.