So this is fun: http://eclecti.cc/hardware/physical-keygen-duplicating-house-keys-on-a-3d-printer

I was actually just thinking along these lines myself last night as I was rekeying my old house. I was thinking more along the lines of milling a key from a stock sheet of metal, but you could probably use this to make a key then copy that onto a real blank.

Then of course there's using a laser cutter...