The "ubuntu-wallpapers" package has just been updated and Ubuntu 12.04 Precise Pangolin now includes wallpapers from the community contest as well as the new default wallpaper:
|Ubuntu 12.04 default wallpaper|
If you're not using Ubuntu 12.04 yet, you can download the wallpapers from HERE.
The wallpapers have a 1920x1280 resolution but if you want, you can download the wallpapers in a higher resolution from HERE.
What do you think?