Well, my favourite fresh water fish.... (or at least ones I've seen)
Angel Fish (I got one, who loves being fed... lots... and lots!)
I had a Freshwater Prawn once... it was cool
Are freshwater crabs allowed? cause they would be different to just the fish (like the starfish was different!)...
Pleckos (cant remember what they are fully called... plekostomus or something), those big dark-grey things that suck the glass etc getting all the moss/mildew off.
Oh.. one I remember, and thought it was awesome.. a freshwater stingray!
It took up the entire tank on its own, but.. it would be cool having one of those on your screen!
Thats my tuppence worth anyway :P