Diversity in Aquaria

A few of us have been tossing around the idea of setting up aquaria
with a diverse population of animals and plants.  This concept
means different things to different people, from setting up a
biotype aquarium consisting of more than just plants and fish
(and algae and snails :-)) to a non-biotype setup consisting
of many different organisms.  "Freshwater Reef" is an analogy
that has sometimes cropped up.

Has anyone attempted anything like this?  I suppose frogs and shrimp
and crayfish are possibilities, as are mussels and clams.  What
organisms can be kept with each other?  What changes need to be made
to the conventional planted aquarium to accommodate these creatures?

Shaji Bhaskar, Durham, North Carolina                   shaji at nando_net