This plugin adds an auto-hide feature to the WordPress Admin Bar that was introduced in WordPress 3.1. Result: more screen real estate and the added functionality of the WordPress Admin Bar.
Download the Auto Hide Admin Bar plugin here: Auto Hide Admin Bar plugin on WordPress.org.
See the WordPress.org plugin page for the changelog.
If you really like this plugin, buy me a beer, or two, or get really crazy and buy me a an electric car.