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.

gilu

NoMoreIE6Please is a widget for WordPress which displays a custom message to update to new browser as specified. You can specify MSIE minimum version 7, meaning, if the user has MSIE 6, a custom message is displayed. Specify Firefox version 13, well, pretty much any Firefox will get this message then.
You can also choose the size of the icons to display, and which browsers you want to show to the MSIE6 user. I.E. disable MSIE and Firefox, then it’ll display only Chrome, Safari and Opera download link.

NoMoreIE6Please

NoMoreIE6Please displays a custom message to update to new browser as specified.

Block IE6 vs NoMoreIE6Please