Andy Charrington

Easily add background options on a per page/post basis.
Currently the plugin includes the following features-
<ul>
<li>Add a background image</li>
<li>Options for vertical & horizontal repeating</li>
<li>Fade out the bottom edge of your background image</li>
<li>Choose background colour</li>
<li>Child pages of a page with a custom background will inherit the parent page background settings.</li>
</ul>

Background Per Page

Background Per Page allows you to set a custom background per page (or post) as well as set up a default background for all other pages/posts.

Marinus Klasen

Different widget content on multiple pages? Exactly.
This plugin adds WYSIWYG editors on page/post level that can be filled with content. 
Add the widget to your sidebar and start editing on page level!

mklasen's Dynamic Widget

Add per-page/post configurable WYSIWYG editors as a widget to your sidebar.

Background Per Page vs mklasen's Dynamic Widget