There are a couple of apps available in the app store that specialize in collecting/sharing iPhone wallpapers. I got one called iWallpapers HD. It's free. It's ok. Big selection but not in the area of sports. If anybody has any idea of a spot where I can locate a selection of SPORTS themed Retina wallpapers I'm sure some other members as well as myself would appreciate it.
I just found the iWallpapers HD app and there are some really nice ones there. I had another app, can't remember the name of it, and they had some cool pics but not hi res ones. It's a shame not to get hi res to take advantage of the beautiful display on this phone!