As far as memorabilia goes, the real-life motion sensing Team Fortress 2 sentry gun that now sits in Valve's offices has to be up there with the coolest.
When we say real-life we don't mean its cannon actually shoots at guests - it does however oscillate before taking out targets with a red flash and a semi-convincing blast sound. That should do it.
The gun was built by the WETA workshop, which has also been tasked with making props for the Lord of the Rings films and Avatar in the past. It even made a real-life Halo Warthog.
Valve announced a public beta for Team Fortress 2 at the beginning of the month geared towards 'testing new technologies' for the game.