Hero System's Champions setting has Monster Island, about to be published. Genre: Supers. Of course, Hero is a toolkit, so you can make the setting anything you want, from Supers to Super-Spies.
Also, you might check out Rifts which has a bunch of that sort of stuff, as well as GURPS. There's an awesome GURPS campaign generator. It takes three random GURPS supplements and mashes them together so that you can create some really outlandish campaigns. Just put 'Aliens' in the "Simple Search" box and see what comes up.