Aaron Axelsen

The Advanced Search Widget is designed to be a replacement to the defaut search widget. The Advanced Search Widget allows you to search for only a 
specific post type and also select which fields to query (title, content, tags).
In addition, it is also possible to place multiple widgets onto the sidebar to search through different custom post types.

Advanced Search Widget

Allows you to add a widget to search custom post types along with other options

Shambhu Patnaik

Category Wise Search Widget plugin.You have option search specific category content.
Features
<ul>
<li>Search post category wise.</li>
<li>Set default category.</li>
<li>Exclude categories in search category field.</li>
<li>Exclude categories with child in search category field.</li>
</ul>
More detail : http://socialcms.wordpress.com/

Category Wise Search

Category Wise Search Widget plugin.You have option search specific category content.

Advanced Search Widget vs Category Wise Search