Lighting is important for your salt water aquarium, not only to show off your beautifu fish, but also as a requirement for some of the inhabitants of your tank.
Now that you have almost everything you need for your saltwater setup, you need to consider your near-term and far-term lighting requirements. If you plan on having a fish-only tank forever, then you only need a single full spectrum bulb. However, if you plan to advance in your hobby and keep more sensitive animals such as anemones, you must carefully select your lighting (and filtration as well). Anemones require very strong, full spectrum lighting, supplemented with actinic blue. The general rule of thumb is a minimum of 3-4 watts per gallon, with the higher values for deeper tanks (greater than 18-24 inches). The standard Perfecto hood will not provide enough light to keep anemones alive (or other light-loving invertebrates for that matter). Even if you think you will have a fish only tank forever, make your llighting choices wisely as many aquarist feel that they need additional challenge once they master a fish only tank and you want to be setup to easily accommodate anemones with your existing lighting.
For a beginning aquarist, fluorescent lighting is probably the best. Metal halide lighting is really for reef keeping and heavily planted freshwater tanks. In any case, if you want or will need something more than a single lamp, your choices are limited. The best thing to do is to build your own hood with custom lighting, or buy one through mail order. Fish store prices usually preclude aquarists from getting proper lighting.
If your tank has a custom fluorescent hood, then you will have 3 lighting choices – normal output (NO), high output (HO) and very high output (VHO). Normal output is sufficient for fish only. Both HO and VHO lamps require special ballasts, are more expensive than NO lamps, and need to be replaced more often.