Halogen. They don't heat up much, still have a good level of brightness, and are usually small and space efficient.

I tried using florescent strips but they heated things up too much. Then I found these neat little triangular (swivel) halogen lights at Lowes. I've have one plugged in for a long time and it gave off very little heat since the bulb is tiny. I plan to use them in the wooden vivs I'll build for my corns.

I'll try to get some pictures of the lights once I get some new batteries for my camera.