fishykid9212,
What kind of lighting do you have? Caulerpa is so easily removed that I don't see why so many people are afraid that it will "take over." If you want something that will grow and benefit your water quality, my vote is caulerpa. C. racemosa/lentillifera both rarely "go sexual" so they are pretty safe, too. Halimeda, Penicillus, Rhipocephalus, and Udotea are very slow growing, non invasive algae that usually grow out of mud / sand. They need lots of calcium and low phosphates, though. Seagrasses might also do well. Maiden's Hair (Chlorodesmis) is another possibility but most people don't have good luck w/ this algae.
HTH,
Kevin