mores

MetaBackGround will let you specify a post background by adding a custom field. This is not the sorcerer’s stone, but some users are not comfortable with php and editing of theme files, so all they need to do is install this plugin.

MetaBackGround

I once created this plugin for someone ... they needed to set backgrounds on a per-post basis.

sammyb

The WP Background Tile Plugin for WordPress applies a tiled background image to your blog. 
It is as simple as this:
<pre><code>* Create a background image
* Upload it
* Apply it as the background via the WP Background Tile options page
</code></pre>
Applying a repeat pattern to the background of a webpage is easily done using css.However, 
if you’re not into writing code, or don’t know where to insert the css into your 
wordpress theme, then you will find this plugin much easier. It can also be an easy way of 
testing out lots of background images before deciding on one you are happy with.
<h3>Usage</h3>
<ol>
<li>Go to ‘Settings => WP Background Tile’ in WordPress</li>
<li>Paste in the URL of your background image</li>
<li>Press ‘Submit’</li>
</ol>
For more detailed info visit the plugin page: http://www.samburdge.co.uk/wordpress/wp-background-tile-plugin

WP Background Tile

The WP Background Tile Plugin for WordPress applies a tiled background image to your blog.

MetaBackGround vs WP Background Tile