shazdeh

This plugin integrates with WP 3.0 built-in Custom Backgrounds, and enables you to choose from a growing collection of patterns provided by <a href="http://subtlepatterns.com" rel="nofollow ugc">Subtle Patterns</a>.
To updaters: Please note, you might need to reselect your chosen pattern.

Background Patterns

Use a library of beatiful patterns and decorate your webpage background.

Kailey (trepmal)

The ability to select an image from the media library as the background is baked right into core now. This plugin will no longer be developed.
Add an action button to images in the media library. Easily use any image as your custom background.
Custom backgrounds must be enabled on the active theme

Get Background From Library

(No longer in development.) Add an action button to images in the media library. Easily use any image as your custom background

Background Patterns vs Get Background From Library