This plugin manages backgrounds, and loads a random one each time. It features a settings page under “Appearance -> random backgrounds”, where you can add and remove backgrounds, and edit the CSS used for displaying backgrounds (you can even use this plugin to load CSS!). It supports using full-width and tiled pattern backgrounds, and you can use your own CSS and HTML to display the backgrounds the way you want them.
Out of the box, it deploys the epic ultra premium Stuff and Dirty Wall backgrounds on your site. You won’t see them anywhere else! (but really, you will want to replace them with your own backgrounds).