Phillip.Gooch

Backdrop is a site background customizer with power greater than the mere stock background selector included with WordPress. What can backdrop do that the default can’t? I’m glad you asked…
<ul>
<li>More than just boring backgrounds, flexible backgrounds, parallax backgrounds, even sliding backgrounds are stuffed in here too (don’t worry, the boring ones are still around as well).</li>
<li>Options, options, options! More options that you can shake a well sharpened stick at.</li>
<li>Uses the WordPress customizer interface so you can see your changes as you make them.</li>
<li>One click HiDpi (or retina) backgrounds, make it look all purdy on that fancy screen.</li>
<li>Theme schmeme, we don’t need support in your stinkin theme, backdrop can force it’s way into nearly any theme.</li>
<li>Calls external JS and CSS files that are appropriately cached.</li>
<li>Advanced options for those in the know with CSS.</li>
<li>Built for the smoothest animations possible.</li>
</ul>
Note: Starting with version 2.0 Backdrop will no longer work it’s magic with older versions of Internet Explorer (before version 10). If you want to support animations on older versions of IE then please use Backdrop 1.X.
Note: Your Backdrop settings will not be transfered from 1.X to 2.X, you will need to re-set your backdrop on update.

Backdrop

Backdrop is an improved site background customizer allowing for all manner of fancy things.

tommygeorge

Super Simple jQuery Parallax Background enables a parallax effect with your theme’s background image. Just set a background image in your theme’s “customize” options (optionally setting it to “fixed” position) and activate this plugin. Done. “It just works.”
It relies on jQuery, which comes with WordPress and is probably built into your theme. Tested and works with the “Twenty Twelve” theme out of the box.
Looks best with seamlessly-tiling background images.

Super Simple jQuery Parallax Background

For themes with background images, creates a parallax effect when scrolling. Super simple; no configuration. Just works.

Backdrop vs Super Simple jQuery Parallax Background