Ramoonus

This plugin adds the Modernizr to your WordPress installation. 
Modernizr is a small JavaScript library that detects the availability of native implementations for next-generation web technologies, i.e. features that stem from the HTML5 and CSS3 specifications. Many of these features are already implemented in at least one major browser (most of them in two or more), and what Modernizr does is, very simply, tell you whether the current browser has this feature natively implemented or not.
For documentation visit http://www.modernizr.com/docs/

Modernizr for WordPress

The 2.8.4 version inserts broken javascript link. I posted a message about this in the support section for the plugin and the author has not responded or fixed the problem. Now, any site that I've added this plugin to can be broken if the user runs an update. 

Instead, if you need Modernizr, insert the following into your header.php file just after <?php wp_head(); ?>:

<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/modernizr/2.8.3/modernizr.min.js"></script>

Doesn't work - Plugin Defunct

This plugin adds the Modernizr to your WordPress installation.

gnarf

No IE Welcome can react to a Visitor using Microsoft IE (Internet Explorer) of a specified Version. You can
<ol>
<li>Slide Down a Infoscreen (changeable CSS Style) where the User is informed that he should update his browser. All Texts and update Links are defineable in admin menu. No Popup is used, so no chance fpr Popup blockers. You can define a time where the Infowindow hides again automatically.</li>
</ol>
and / or
<ol>
<li>You can use a different WordPress Theme for these users. It can be a Theme that is optmized for IE, or a Theme where you suggest the user to Update / Cange Browser and so on. </li>
</ol>
For Users not affected by the Plugin the source code is not changed. So the Plugin is highly performant and a non IE User doesnt notice the use of the plugin at all.
Easy Installation and configuration.
Also visit the <a href="http://wordpress.losmuchachos.at/no_ie_welcome" title="Plugin Page" rel="nofollow ugc">PluginPage</a>.

No IE Welcome

No IE Welcome allows you to inform Vistors of a specified IE Version to Update their Browser. Also a different Theme can be used for these Visitors.

Modernizr for WordPress vs No IE Welcome