Admin Bar Hover Intent is a plugin by ryanimel that slows down the dropdown effect of the WordPress Admin Bar. By default (as of WordPress 3.1.x) the WordPress Admin Bar reacts to any mouseover by dropping down menu items. With this plugin you have to hover over the menu items deliberately in order for them to display.
No configuration is needed.
Download and info: http://wordpress.org/extend/plugins/admin-bar-hover-intent/