I personally wouldn't go with exodons...They are a waster of time..With most if not all of the other suggestions you could keep something with them if you wanted while exos are just a species only of pretty ugly fish...Most people I know who went with exo's in a decent sized tank have regretted it...
I personally would go for one of the larger species of rainbowfish, my fave being the reds, or a shoal of angels or discus
Corydoras are probally the coolest shoalers and there is so much variety. They are truely awsome fish