Arindo Duque

Are you already tired of the way WordPress 3.8 looks?
Did you wish to be able to change and personalize, and even whitelabel some of the WordPress signatures on the WP Dashboard?
Note: We are officially returning to support his plugin, so <a href="http://weare732.com/en/home/#av_section_4" rel="nofollow ugc">let us know</a> if you have any feature suggestion or bug you want to see solved. A major release with a bunch of new features should be arriving soon.
Well, you can do all of that with Ultimo WP!
With Utimo WP Dashboard Theme you can:
<ol>
<li>Personalize the entire look and feel of the WordPress dashboard, based on 8 beautifully designed presets (and counting).</li>
<li>Personalize the login screen of the WordPress dashboard.</li>
<li>Whitelable some of the WordPress signatures, like the footer texts and adding your company logo to the dashboard and login page.</li>
</ol>
<a href="http://codecanyon.net/user/732/portfolio?ref=732" rel="nofollow ugc">Check out my premium plugins!</a>

Ultimo WP

Get a clean, beautiful and customizable new look on your WordPress Admin Dasboard.

Arun Basil Lal

A simple plugin that lets you add your custom CSS to style the WordPress Admin. Works with WordPress single install and WordPress multisites.
Version 2.0 is updated wtih an Admin interface and can be found in Appearance > Admin CSS MU
Admin CSS MU uses CSSTidy to clean and optionally minify CSS. CSS is only minified while using it. The editor always shows un-minified CSS for easy editing.
Note: If you want to easily add custom CSS on your Login and Front-end as well (along with WordPress Admin), use my <a href="https://wordpress.org/plugins/custom-login-admin-front-end-css-with-multisite-support/" rel="ugc">Custom Login Admin Front-end CSS</a> plugin instead.

Admin CSS MU

Good plugin

Add custom CSS to style the WordPress Admin. Works with Multisites.

Ultimo WP vs Admin CSS MU