The Utili-Key 6-in-1 Tool from ThinkGeek is about the size of a normal key, when it's all folded up anyway. They've manage to pack in a flathead, Phillips head and eyeglass screwdriver, a semi-cerated knife (which I guess counts as two blades), and a church key!

It's a bit generous to call this a 6-in-1 tool, I think, but it doesn't make it any less cool. I think I've found the perfect thing to replace that falling apart pocket knife I've currently got on my keychain!