For those interested in more Gamma World origins, there is a pretty good effort on the WotC forums to compile user-made origins. You can check it out at http://community.wizards.com/go/thread/view/75882/26075109/Custom_Origins_Compilation.
Some of my favorites concepts from the thread are Amphibian, Avatar, Cosmic, and Dimensional. Amphibian makes me want to see some Battletoads characters. Avatar nicely encompasses the idea of being a willing vessel for a powerful entity, but it could be pretty easy to reskin as being involuntarily possessed. Cosmic is for beings composed of only light (think living stars) and has a nice set of powers to support the theme. Dimensional is a nice wacky concept, but the mechanics for it seem like they might be a little overpowered.
My Two-Headed origin is also included in the second compilation pdf. In addition, the first compilation pdf includes alternate takes on shark and dinosaur origins (as Sharkoid and Saurian).
Scott's Game Room 
One reply on “Community Origins Compilation”
I like your continued attention to customizing GammaWorld. I doubt my group will play it much after our first try, but it still intrigues me, and you keep inspiring me to try my hand at creating some of my own wacky stuff. Thanks.