digitalapps

This plugins detects all of the styles queued via wp_enqueue_style. Contents of each css file are copied and stored in a single css file. This file is loaded on the frontend. The plugin wp_dequeue_style and wp_deregister_style all other css files. The result is your website only makes one single http request to load css styling. Bonus feature the contents of the css file are minified.
Simply flip the switch and the plugin will do the rest.
NOTE: I have only tested this plugin on my own sites running the AdSense Theme. If you encounter a problem with this plugin please let me know. I will be able to help you.

WP CSS Merge

This plugins detects all of the styles queued via wp_enqueue_style. Contents of each css file are copied and stored in a single css file.

Sean Michaud

Optimize Scripts & Styles optimizes your site’s JavaScript and CSS files by combining, minifying and caching them. This will help your site’s overall performance and user experience by reducing the number of files served up and the overall size of these files.
For developers, this allows you to maintain uncompressed versions for development themes or plugins, while compressing them for a production environment.
For you SEO buffs, it cleans up the number of scripts that get included and downloaded to your site visitors, helping your overall PageSpeed score.
Header and footer script locations are maintained as well as any localized data used for the scripts and the minified files are stored in the /cache folder, making it friendly for plugins like WP Super Cache. Media attributes are also maintained for print stylesheets.
<h3>Features</h3>
<ul>
<li>Combine & minify all JavaScript & CSS that is enqueued</li>
<li>Stores the optimized files in the cache folder for faster page loads</li>
<li>Compatible with caching plugins like WP Super Cache and W3 Total Cache</li>
<li>Enable for logged in users (not recommended)</li>
<li>Available options to remove or ignore enqueued scripts and styles</li>
<li>Optional button in the admin bar to clear scripts and styles</li>
<li>Includes an option to remove script type attributes for HTML5 validation</li>
</ul>

Optimize Scripts & Styles

Optimize Scripts & Styles combines scripts and styles on your site, minifies them and provides cachable versions for improved site performance.

WP CSS Merge vs Optimize Scripts & Styles