PonySiege
It isn't nearly fluffy enough... missing that horn on its forehead... and it's not riding on rainbows... This should be fixed-lenir
What I'm trying to say there is (obviously) that FreeSiege (git repo here | screens here) is looking for help updating the assets (and they're looking for an awesome horse I think).
So if you know any freely licensed one.. can and want to model one yourself.. or perhaps want to improve the pony (see quote above).. here's the thread to go to. :)
In other news: GameKit 2 is now available on the Blender wiki.