dwieeb

With this plugin, you will be able to include certain CSS or JS files in only selected posts, pages, or other post types, instead of including them everywhere. You can also edit inline CSS & JS and include CSS & JS files from anywhere on specific posts and pages.
It places meta boxes in the WordPress post editor so it’s easy to select which files you want to include with the post you’re currently editing. This plugin works well for all websites, large and small, and it works well with WordPress multi-site (WordPress MU). Tested up to 3.1 beta 2.
See this plugin’s <a href="http://www.danielimhoff.com/wordpress-plugins/specific-files/" rel="nofollow ugc">page</a> on my website for information/comments/questions. I am open to the idea of suggestions and patches to this plugin! If you enjoyed this plugin, please <a href="http://www.danielimhoff.com/donations/" rel="nofollow ugc">donate</a> or <a href="http://www.danielimhoff.com/donations/" rel="nofollow ugc">say thanks</a>.
Todo:
<ul>
<li>Add a “remove references” button on the options page so people can remove file references without having to delete the file.</li>
</ul>

Specific Files

This plugin allows you to include CSS or JS files in specific posts and pages.

esthertyler

Transfered to new dev: https://profiles.wordpress.org/esthertyler
Maked by Esther Tyler: http://mycustomcss.com/
With this plugin you can put custom css code without edit your theme and/or your plugins (really useful in case of any theme/plugin update).
It contain also <a href="https://ace.c9.io/" rel="nofollow ugc">Ace (Ajax.org Cloud9 Editor)</a> Code Editor for write a good css code.
You can see in action (source code) here: <a href="http://www.vegamami.it/" rel="nofollow ugc">VegAmami</a> 🙂
PS: support file backup and – very important – static css file (fantastic for performance) 😉
<h4>Links</h4>
<ul>
<li>New dev: https://profiles.wordpress.org/esthertyler</li>
<li>Author Homepage: <a href="http://mycustomcss.com/" rel="nofollow ugc">Esther Tyler</a></li>
<li>Plugin maked for (demo link): <a href="http://www.vegamami.it/" rel="nofollow ugc">VegAmami</a></li>
<li>Ace (Ajax.org Cloud9 Editor): <a href="https://ace.c9.io/" rel="nofollow ugc">Ace (Ajax.org Cloud9 Editor)</a></li>
</ul>
<h4>Language</h4>
<ul>
<li>English</li>
<li>Italian</li>
<li>Full translatable!</li>
</ul>

My Custom CSS PHP & ADS

Enable to add Custom CSS Code via admin panel with Ace (Ajax.org Cloud9 Editor) + backup (see screen) and static file cache (best performance) :)

Specific Files vs My Custom CSS PHP & ADS