I don't know much about this stuff because, like you, I wasn't quite sure where to look, but after some research and instead of doing a retro-fitting project, last week at my LFS I got a new Coralife 24" double flourescent light w/two 14 watt slim flourescents on it to put on my cheap plastic hood that came with the starter kit I got.
I got it b/c I wanted to increase my wattage from <1 to about 1.4 wpg currently. It was about $52 at my LFS. No matter how I worked it, upgrading my lighting was going to cost me about that much to make a change, so I went with the one piece for a cleaner look instead of buying a new glass hood and a cheaper light to add to the one I already had, which would have looked like a messy hodge-podge. What's cool about it is that it's very slim. The problem is that it doesn't quite fit the old hood perfectly, so some light escapes and reflects onto the wall behind the tank. It's really no big deal, however, and it is made with little extension bars to slide out and rest securely on whatever type of hood or tank you have.
Anyway, I like what I bought and would recommend it. As far where to get it, I have no idea. Check out Big Al's or other large online retailers. Or if you have a good LFS, see what they have.
