Most people today are leaning towards HOT5 fixtures with individual reflectors. They provide enough light to keep any type of coral. Unless you want clams on the bottom of a tank that is 24" or taller they will be a great option.
Bigger is better. If you can go 6' long, get a 125. If you are stuck with 4' length there are 4' tanks that are 110, 120, 150, and even 200 gallons.
It is VERY important though to stick to a tank that is small enough that you can afford to do it right. I have seen many people get big tanks cheap on craigslist or save up and buy a big tank, but then they can't afford a proper lighting system, filtration, skimmer, enough live rock, etc. A properly setup tank will run better than a larger tank that is not setup as well.
Are you wanting a reef?
FYI my tank has 4x96 watt compact fluorescents on it and I have SPS
, clams, etc. With enough of them you can get enough light in the tank. But HOT5 fixtures with individual reflectors are a better buy if you are buying new.