If you're a Halo fan, you're going to want to check out Conflicting Gamers latest Windows Phone Wallpapers and Theme. Much like theo L.A. Noire and Portal 2 wallpapers and themes, there are four transparent wallpapers to choose from as well was eight Live Tiles and four Picture Hub backgrounds.
And they look really good.
You can download the complete set over at Conflictinggamers along with directions on how to install each (it's really easy). As much as my son plays the Halo series, I'll probably download the Master Chief to use as his Contact Photo.