Janar

With this plugin you can add extra HTML or just plain text when posting a new page or post. That content will be displayed in sidebar widget. It is tested from WP 2.6 to 3.0.1.

ax-sidebar

With this plugin you can add extra HTML or just plain text when posting a new page or post. That content will be displayed in sidebar widget.

itcoderr

This plugin gives you a way to choose what widgets display on each page/post of your website. The plugin’s custom sidebars provides a way, using that you can display custom widget configurations on any page, post, post type, or archive page.
Features
<ul>
<li>Unlimited custom widget configurations</li>
<li>Custom widget for individual post, page etc..</li>
<li>Sorting sidebar</li>
<li>Many more</li>
</ul>

Acquaintsoft sidebar generator

Create custom widget configurations for every page/post on your website.

ax-sidebar vs Acquaintsoft sidebar generator