John

This plugin enables you to manage your projects from the WordPress interface you are already comfortable with. Easily create and track the progress of projects and tasks.

WP-Trac

This plugin allows users to manage projects and tasks.

ggwicz

Simple Todo List is a widget for your WordPress dashboard that lets you keep track of todos in a simple, intuitive list.
Features
<ul>
<li>Simple AJAX interface in one self-contained Dashboard widget.</li>
<li>Simple Markdown-style formatting enabled; use * or _ for italic text, and ** for bold text.</li>
<li>Coming soon: live inline-editing.</li>
<li>Coming soon: simple drag and drop reordering.</li>
<li>Coming soon: code improvements.</li>
</ul>

Simple Todo List

The simple todo list is easy to setup and use. Unlike others todo list plugins, this one is non-obtrusive. Although functional, it would be nice to see some additional features offered:

Automatically group completed todos to bottom of list.
Automatically hide completed todos.
Option to toggle show/hide completed todos.



Pretty Easy, But Feature Short

The missing todo list dashboard widget for WordPress.

WP-Trac vs Simple Todo List