You can fit any type of lighting on top of almost any type of tank.
If the tank is less than 24'' deep, you can use Power Compact Flourescent (PC) or T-5 Flourescent. They both have the same quality of light, despite what some whacked-out people might tell you
Some people seem to have this wierd idea that T-5's are better, but both PC's and T-5's use the same technology. It's just that T-5's are newer. PC's actually tend to have a little more "brute force" to their light. T-5 lighting will never sell me, because they seem to me to just be upgraded flourescents, and not anything new. But both lighting types are fine for a small reef tank.
If the tank is deeper than 24'', it is best to use Metal Halide (MH). MH appear similiar to hulked-out incandescents, but are very valuable to a reef tank for their incredibly high capacity. They are also very beautiful because of the way they concentrate light. It produces a "wavy" effect as it reflects off the ripples in the water that is very similiar to the effect natural sunlight produces. It is benefitial to the tank's inhabitants, because it is natural, and it is also stunning to look at
You can choose between two types of MH, Mogul-based fixtures and HQI (I don't know what this stands for
) . Moguls are able to support an immense wattage (I have seen Mogul-based MH lights rated at 1000 watts) and are single ended. HQI tend to produce more light per watts, and are double ended. I have not seen HQI beyond 250 watts.
Do more research, and get what you want
-Lynden