You could put one or two african butterfly fish in. they are definately odd looking. those would stay at the top of the tank, so could still find some cool bottom dwellers like a crawfish or something.
there are more than 20 fresh water pufers, plus you could add a polypteus senegalus albino, that whould look awsome with the smaller tipe of puffer an maybe somethig odd like a knife fish or a calabricus...