Do you have any idea of what specifically you want in terms of corals? In general, if you wanted the strongest lighting (not necessary for all corals), you would go with metal halide, but they are expensive, and aside from cost, there are other logistical concerns, such as if your setup can accomodate them without overheating water, etc. There are other options as well, including power compact & VHO (very high output fluorescents), that work very well for many corals. Read some of them in the articles here on RC.