GnomeArt NextGen is a small application which can take care of all your styling needs in the Gnome Desktop environment. It offers a wide range of Backgrounds/icons and theme collections which you can use to add eye-candy effects to your Gnome Desktop.
Here are the steps to install it in Ubuntu, simply download the matching installer file for it from here. Once the file is downloaded, run the following command to install it.
sudo dpkg –i DownloadFileName
Replace DownloadFileName with the name of the file that you downloaded.
sudo dpkg –i gnomeartng-0.6.0-all.deb
Once the installation is completed, launch the application from Applications -> System Tools -> Gnome-Art Next Gen.
The left side bar lists the items which you can change using this tool. Choose Backgrounds, Icons, Splash screen, etc and you will get its respective available choices in the main window. It can show images of multiple image types and resolutions, select the desired image, hit Apply and you are done. Enjoy!