remm

This plugin provide widget that display a list with categories and posts in your sidebar. 
Widget can save the opened categories, and use cache.

Wp Ajax Tree

This plugin provide a widget that display a category and pages tree on your sidebar, using ajax to collapse categories.

Cynob IT Consultancy

Using this plugin, you can put horizontal image slider with the help of shortcode used after installing plug in.
Plugin Features 
<ul>
<li>Shortcode System.</li>
<li>Touch Enable.</li>
<li>All Browser support.</li>
<li>Auto play Enable.</li>
<li>Unlimited Carousel.</li>
<li>Use via short-code.</li>
<li>Support post or page.</li>
<li>And many more.</li>
</ul>

Horizontal Carousel

Using this plugin, you can put horizontal image slider with the help of shortcode used after installing plug in.

Wp Ajax Tree vs Horizontal Carousel