Gecka

Display a configurable warning for Internet Explorer upgrade.
Choose to display the warning for versions before IE8 or before IE7.
Choose to always display the warning, or once per session, or once a day, or every 30 days or every year.
The plugin configuration appears in the Reading Settings page.
(based on <a href="http://code.google.com/p/ie6-upgrade-warning/" rel="nofollow ugc">ie6-upgrade-warning</a>)

Gecka IE Warning

Display a configurable warning for some versions of Internet Explorer

lupomontero

This plugin replaces the contents of your site with a message asking your 
visitors to use a better browser if they try to browse your site with Internet 
Explorer 7 or earlier.

No IE

'No IE' blocks visits from Internet Explorer 7 and earlier and displays a nice message with a list of better browsers.

Gecka IE Warning vs No IE