This plugin allows you to select multiple backgrounds, and display one each page.
Random backgrounds, as simple as possible! Just add your background, choose if you want to stretch it, tile it, or use custom HTML to display it. Find the settings under appearance -> random backgrounds. You can also set your own CSS for the random backgrounds. The plugin uses the WordPress image uploader to upload and insert images, and allows you to set as many images as you want. It also uses config files instead of MySQL, for superior efficiency in most server configurations.
Out of the box it deploys the Stuff and the Dirty Wall backgrounds, which are especially designed to make you want to delete them, so you will be familiar with the settings panel.