I have a miniature sliding switch with 3 pins, I just soldered negative to the end pin and positive to the middle pin. I then covered the remaining exposed pin in hot glue to avoid any misdemeanours, and so if i removed the switch i knew which pin to use again. It's not a really clear photo, but you can see it in my picture here.

Unfortunately i'm in the UK, and I can't actually find it on their website, but my local Maplin (electrical hobby store) had one on the shelf, was about £2.

:: Edit - Switch I purchased is this one (it is tiny) ::