Depends on what you want to do with it.
If you plan on a refugium than some nice macro algae and some rubble rock would be a nice addition and provide a home for pods and other critters.
I get most of mine from my LFS. Ask for calurpa (sp) or Halimida. There are quite a few varieties. There is a place in Hawaii that sells some more exotic types. Email me if you want the link. r_hyatt@hotmail.com
Another option is finding someone that has alot of excess and work out a deal with them. I used to throw away tons of halimeda every month.