Brian Zeligson

This plugin uses the wp_print_scripts action hook, as opposed to output buffering and regex used by alternative implementations.
The downside of this method is that only scripts loaded via wp_enqueue_script will be affected by the plugin, the upside is better 
performance by avoiding output buffering on every page load.
The plugin will preserve any localizations added via wp_localize_script, and uses the first parameter passed to wp_enqueue_script 
as the label for the script in the head.js call. For example,
<pre><code>wp_enqueue_script('jquery', 'https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js');
</code></pre>
would show up as
<pre><code>head.js({"jquery": "https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"});
</code></pre>
This allows you to run callbacks when specific scripts are ready, such as
<pre><code>head.ready('jquery', function() {
 //do something when jquery is loaded
});
</code></pre>
For more on HeadJS usage, see http://headjs.com/

WP HeadJS

Uses HeadJS to load your enqueued scripts asynchronously, in parallel, executing them in order.

kylereicks

Head.js is a script to asynchronously load and manage dependencies of javascript and CSS assets.
This plugin loads the scripts and styles enqueued in footer with the head.js loader. It does not include head.js’ feature detection.
Head.js.wp assumes that scripts are loaded via <code>wp_enqueue_script()</code> and that any script enqueued in the <code><head></code> intends to be loaded before the rest of the page.

Head.WP

Head.js is a script to asynchronously load and manage dependencies of javascript and CSS assets.

WP HeadJS vs Head.WP