An excenellent communal species would be T. stigmurus, and all of the other closely related species. I have 3 adults - all different sizes - in a tank with about 20 babies. Can't go wrong with them. There's also C. sculpturatus, C. vittatus, V. carolinianus. which all easily obtainable. P. reddeli is also a good species to keep I hear. Keep food plentiful and give plenty of space and hides for them.
