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.

Hans-Helge Buerger

Child Page Tree adds a select box to the page edit site right above the publish button. Using this select box you can decide whether to add and where to add the page tree. You can either add the page tree at the very top of page (prepend) or add it to the end of a page (append).
The output is a unorderd list with nested lists to reflect the hierarchy of the children. However this list can be changed using the build-in filter <code>child_page_tree_before_output</code>. This filter is applied before the list is added to content.
The plugin ships with basic stylesheet, which adds a icon to each link and does not show the hierarchy of the pages. The handler for this stylesheet ist <code>child_page_tree_style</code> and you can simple dequeue the script using <code>wp_dequeue_style()</code>. Another way to add your own custom style is to override the default style by using a custom CSS plugin. The page tree has an id (<code>ul#child_page_tree</code>) you can use and one class, either <code>.append</code> or <code>.prepend</code> depending its location.
<h4>Requirements</h4>
<ul>
<li>min. PHP 5.4</li>
</ul>

Child Page Tree

Very minimalistic and useful plugin. I like it!



Very useful

Display a page tree of all child pages of the current site

Wp Ajax Tree vs Child Page Tree