Again it depends on what you want to keep. The watts per gallon is just a guideline, not a rule. Especially true when factoring in T5s which are designed to give off greater light with lower watts than a typical flourscent.
High Light Demanding Species: MHs or T5s with individual reflectors
Fish and species that don't use light for "food": any old non UV light
Things in between such as LPS and Softies can get away with a variety of things, best to figure out what you want to keep in the near future and then get the lighting to support it