Honestly in the back of my mind, I'd like to see how diverse an "ecosystem" I could create. Right now I've got: Shrimp (2 species), Copepods, Flatworms, Tubifex worms (I think ?) and 1-2 species of snails. I'd love to add more but not sure what else would work. Fish are out I think b/c they eat so darn much....
and of course who know what kind of micro-fauna I've got.