Vast HTML

This plugin keeps people from viewing your site if they are using Internet Explorer 6. Gives options to download a variety of newer browsers.
For more information on the plugin visit: http://vasthtml.com/js/wordpress-block-ie6-plugin/

Block IE6

This Wordpress plugin will block IE6 users with a choice to upgrade.

sara cannon

Twentyten is the default theme for WP 3.0 and has beautiful CSS for its menu system. However, if you wanted your menu to drop down in IE6, this does not occur. Use this plugin to make that happen using the jQuery built into WordPress. Many people don’t care about browser compatibility back to IE6, so this plugin is for the few that happen to.

Twenty Ten IE6 Menus

Use this plugin to make the main menu in the twentyten theme drop down in IE6. Perfect for Child Themes.

Block IE6 vs Twenty Ten IE6 Menus