I used a 6 amp 125 VAC toggle switch from Radio Shack. I put it in facing down in a pre-existing hole on the bottom of my dash so I wouldn't have to drill any holes in the face (!!!).
Just a suggestion, pick up a 6 or 12 volt (depending on your truck's voltage) buzzer while you're there, and wire it in parallel with your backup light somewhere behind the dash. It'll sound really annoying when you're backing up, but it'll keep you from accidently driveing down the road with your backup light on and getting pulled over.
