This seems to be one of the most confusing parts of the hobby. First off you need to decide what type of corals to keep. If you go with low to moderate lighting. (for your tank 4 40 watt std flourescents half actinics) you could keep stuff like mushrooms and soft corals, some of the hardy large polyp stony corals like pearl bubble or red/green brain. If you upgrade to 4 X 96 watts power compacts or 2 X 175 watt metal halides and actinics you could get away with giant clams and small polyp stony corals like acropora. I would read a lot of books about lighting/corals and go real slow before you buy any light fixtures so you can get just what you want out of your tank.