I like bahaman anoles for small tanks. People say they're not good "pets" but i've had them before and i think they're pretty neat. As long as you dont plan on handling them and you have REALLY sharp reflexes, I think it'd be pretty cool. You can pick a couple up for about $5 - 10, depending. Careful when you're cleaning the tank though. They're lightning fast and if they get out, chances are you won't see them alive again.