Adrian Hanft

The Browser Specific CSS plugin is a tool that allows developers to easily target different browsers straight from the stylesheet. Browser Specific CSS adds a short javascript to the head of your page that enables you to use browser specific css selectors. For example, targeting Internet Explorer 7 from your stylesheet is just a matter of defining styles with a “.ie7” selector. Every major browser is supported including code for targeting Macs, PCs, and Linux operating systems.
This plugin uses the javascript written by <a href="http://rafael.adm.br/css_browser_selector/" title="Rafael Lima" rel="nofollow ugc">Rafael Lima</a>. No changes have been made to his code, and all the credit goes to him. Thanks, Rafael!
Changelog: 
Version 0.3 
– Update for compatibility with WordPress 2.9
Version 0.2 
– Corrected readme file.
Version 0.1 
– Features of the first version of this plugin include the ability to turn the plugin on and off and to specify a separate stylesheet.

Browser Specific CSS

The Browser Specific CSS Plugin allows you to easily target specific browsers and operating systems from your theme's stylesheet using regular cs …

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

Browser Specific CSS vs Gecka IE Warning