I just set up an 18x18x18 pygmy viv and used:
Ficus benjamina (I found very small one, about 15" high for $8)
Rubber Plant (Ficus elastica decora)
Croton (safer for pygs than other chams that might munch on it)
Two others that I don't know the name of... one is like a little palm, I've checked it before and it's safe. It's a great filler and is really hardy.
Schefflera arboricola and small bird's nest ferns are nice as well, but I had no room for them.
This http://www.flchams.com/safe_plant_list.asp is the best plant list I've found.