(Only a few of the pr09studio wallpapers - using different colors)
The guys at pr09studio have an amazing abstract wallpaper collection which you can check out here. Some are Ubuntu / Linux / Gnome / KDE branded but there are also unbranded wallpapers (yes, I know, some of you don't like branded wallpapers).
If you don't like the default color for some wallpapers, you should download the archive anyway since some of them come in lots of different colors (like you can see in the screenshot above).
Download the wallpapers @ http://pr09studio.yolasite.com/wallpapers.php
Thanks to Ubuntu Life for the link!