John Godley

A very simple plugin that adds a drop-down listbox to the bottom of multi-page posts. The purpose of this box is to allow the user to jump directly to a named page, rather than navigating using page numbers.
<h3>Documentation</h3>
Full documentation can be found on the <a href="http://urbangiraffe.com/plugins/jumpto/" rel="nofollow ugc">Jump To</a> page.

jeff.cave

This plugin provides a “Sub Page” widget. It lists all of the pages which are children of the current page. If there are no children, it will not display.
Options include:
<ul>
<li>title (obviously)</li>
<li>“No Sub-pages” text instead of blank (configurable)</li>
<li>hide widget when no sub-pages</li>
<li>show siblings when no sub-pages</li>
</ul>
While this is a small widget, I have attempted to make this as configurable as possible, with clean and efficient code (this is a small widget, and shouldn’t slow your site down).

PS Sub-pages

Shows the child pages of the current page. Configurable title, show siblings (or not), and "no child" text

Jump To vs PS Sub-pages