Debug Bar adds an additional debug menu to the admin bar integrating extra debugging features showing, query, cache, and other helpful debugging information.
When WP_DEBUG is enabled it also tracks PHP Warnings and Notices to make them easier to find.
The plugin requires WordPress 3.1 as it hooks into the new Admin Bar.
Peter Westwood a WordPress developer has posted additional info at: http://westi.wordpress.com/2011/01/05/introducing-debug-bar/
Plugin download: http://wordpress.org/extend/plugins/debug-bar/
