i would suggest the calcareous algae--<em>Halimeda</em>, <em>Udotea</em>, <em>Penicellus</em> and others--as good ones. some other <em>Caulerpa</em> are quite decorative, but you have to take care to keep them well-nourished and pruned (and don't let them get into the sea!).
if you look back through old threads on this forum you will find a lot of good selection and culture information.
