That seems like a medium large kind of enclosure to me. You could house one really big arboreal tarantula species, a small group of tree frogs, a group of medium to small geckos, can't really think of any adult arboreal snakes small enough to live in that size really. It could house a sub adult green tree python, or amazon tree boa sized snake no problem but you'd need to get a larger tank for those species as adults.

Should be noted that you'll have to look through each species of the groups I mentioned to see what are okay to house together. Some species can cannibalize and you don't want that. :/

You have quite an exotic collection already, surprising your question is related to such a small viv when your space requirements will be somewhat different soon enough! However if I was as as abitious and as curious as you (and my family would let me have more space in the apartment i pay for) i would go for Dart frogs! Never kept them myself (had the books for years) but setting up a beautiful habitat for them must be a fantastic and rewarding challenge. Feeding them is another problem however..alternativley perhaps a small species of chameleon or a vine snake (but i think the latter would need more space..yeah, go for dart frogs (or simply a couple of tree frogs). Dart Frogs, Dart Frogs!!!

Have you ever been hypnotised? Dart frogs!

It does sound like a good size for dart frogs. Just don't lick them. Or do. I'm not your mom.

Oh yes dart frogs would be pretty in that enclosure! Or maybe reed frogs?