I use regular florescent bulbs. Incandescent can get too hot in spots, and CFL are expensive. Recent research (I read) said that plain florescents work just about as well as full-spectrum lights with not enough difference to warrant the added expense.
CFL for sure. Incandescent bulbs don't produce the enough of the light plants like, and they get hot and will burn your plants.. Back to the CFL's... you need to have about 4 - 100 Watt, or 8 - 60 watt equivalents for a 48" shelf. Here is a picture of something we made up to contain the bulbs. (Grow fixtures can be expensive, but all you really need is the sockets) We found this fixture at HOBO for $5, we found the lights at Walmart - 4 for $1.89 (60 watt equivalent) You want the Daylight bulbs, At least 5,000K higher the better.
If you have the space you should go for HID lights. I prefer metal halide. Check craigslist for high bay fixtures. Try to get the 400Watt ones. I found mine for $20 a piece bulb and all. Try to find one with a plug already wired, or else you will need to know someone that knows electrical to wire in a plug for them.