If you're a graphics designer and want to show-off your talent with Ubuntu, well there's a certain protocol that has to be followed before you can send your "baby" :D to Ubuntu art-work team for consideration.
Anyhow, since we're like 12-11 days away from the official launch of Ubuntu 11.10, the latest news is that 14 brand-new wallpapers just appeared in the Launch-pad page. Although they may not be the official wallpapers pack... but still most of them would make it to the "official" disk images, I think (cannot remember the whole procedure :D).
If interested (heck ya you are! :D), you can get the package from this Launch-pad page. Enjoy!.