If you look in the greenhouse and terrariums forum (or whatever it's called) there's some threads stuck at the top that have more info on lights than you can possibly need.
If you just want a simple answer, as has been said (mostly summarizing):
- No incandescents. They are an abomination of inefficiency and waste. Plus the heat will cook your plants.
- You want fluorescents of some kind. There are three options.
1) Buy that fluorex light everyone here worships (i've heard of sun worshipers, but this is definitely odder yet). It is in a reflector that will fit well over a 10 or 20G terrarium. 65 watts of fluorescent light over a terrarium that small will make it very warm and very bright in there, though. Maybe too much so. I have a fluorex and it is good for some uses, but i would (and do) stick with option (3) for a terrarium.
2) Buy an ordinary compact fluorescent bulb (the kind that screws into a socket, just like an incandescent). Buy the one with the most lumens you can find at the hardware store or Home Depot/Lowes. This will be the cheapest option, but less light. You can buy one of the shiny metal clamp-on reflectors they sell there for about $10 as well, if you like.
3) Buy shoplights or some other straight-lamp fluorescent fixture. If you go the shoplight route you'll have a longer light than you need. That's good. Put more plants under it. 8) Also if you go the shoplight route, get the HD brand (can't remember what it's called- Commercial Electric, i think) that is about $15 and takes the smaller (not shorter, thinner) T8 tubes. It will be brighter, cooler, and last longer than the big kind of lamps (T12s).
Have fun