there are small species of iguana out there i honestly don't know what the smallest species is or how big they get but considering they don't get big then why not? May be worth having a look up about, but it would need to be let out alot. What would I do with a tank that size? I'd probably get a little 'troop' of leopard geckos LOL. Or maybe set it up for some tokays if you don't mind not handling them? Failing that, sand boas. Honestly don't know their eventual size or requirements but from my understanding they don't get big, don't quote me on that but it may be worth looking up 
