WP-Backgrounds Lite is a free plug-in by noPlugs that allows fullscreen background images for all posts and pages. Compatible with all major browsers and very easy to install.
Set fullscreen background images for posts and pages
Option to deactivate WP-Backgrounds Lite for certain pages and posts
Compatible with all major browsers like IE7, IE8, IE9, Firefox, Opera, Safari, Chrome and other modern browsers.
Can be used with nearly every theme (premium and free ones). For the most themes it works out of the box (i.e. for TwentyTen or boxed themes). A z-index and a background color option helps you to adjust the background layer and the color.
Vertical & horizontal image centering
Small fingerprint, only a few kb filesize
Easy installation, works out of the box
Option to adjust the background layer (z-index).
Plugin homepage: http://demo.inoplugs.com/
There is also WP-Backgrounds Premium which offers a lot more features (flickr support, background slideshow, pattern, custom login panel, etc.).
http://inoplugs.com/projects/wp-backgrounds-plugin/
Download and info: http://wordpress.org/extend/plugins/wp-backgrounds-lite/
