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.

David Gwyer

Update: As of May 2012 the To Do List Plugin has undergone a complete rewrite and is now fully compatible with the latest version of WordPress (3.4).
Maintain an active to-do list for every registered user on your site! Each list is unique and is automatically displayed for the currently logged in user via the WordPress dashboard.
Administrators have direct access to ALL to-do lists.
Please rate the Plugin if you find it useful, thanks.
See our <a href="http://www.presscoders.com" rel="nofollow ugc">site</a> for more Plugins and themes.

To Do List

Finally, a simple way to keep track of important tasks and activities! Every registered user can maintain an individual to-do list using the built-in  …

WP-Trac vs To Do List