Thoughts..
center console (hiden, exposed, on the side, etc)
reed switch can be activated by a magent - yo can put that most anywhere hidden (i have seen them in exterior mirrors so you can get into teh car).

Neatest hing i think is the new caddy - NO KEY at all! You have a wireless transmitter and when you get so close to the car it unlocks. move away and it locks in 30 seconds. there is a starter button, no ignition key works on teh remote too. You can get this type of system for alarms, so the parts should be avalibale to make it work with locks. You can have the doors lock when teh car is in gear or when teh parking brake is off, most anything that can trigger a switch.

If you are just lookig for cool switches, grab a copy of a rod magazine (as in NSRA magazine, Rod and Custom, etc) and look at some of the ads for power windows and lock conversions -then check out their websites. Lotsa choices.