Travis Smith

WordPress’s themes are absolutly amazing, except you are not able to theme the login pages very well. Smithers Login is a light weight plugin that will allow you full theme control over the WordPress Multisite login pages. This plugin allows for different custom login screens on a single WordPress 3.0 Multisite with Domain Mapping. This Network Activated plugin enables you to specify a stylesheet to be used with every multisite login page allowing for custom login images and messages.
Some Features:
<ul>
<li>Specify CSS style sheet for login pages.</li>
<li>Change the URL and TITLE of the header link.</li>
<li>Add a custom image to the login page with PSD file.</li>
<li>Add specific messages to the different login pages (Login, Registration, Forgot Password)</li>
<li>Change various error messages on login and registration pages.</li>
<li>Enhances and extends DBD Login Style.</li>
</ul>

Smithers Login

Add style to your WordPress multisite login pages! This plugin enables you to specify a CSS to be used on the login page with a custom image/messages.

dubhunter

WordPress’s themes are absolutly amazing, except you are not able to theme the login pages very well. 
DBD Login Style is a light weight plugin that will allow you full theme control over the login pages. 
It also offers additional DIV tag creation for custom messages.
Some Features:
<ul>
<li>Specify CSS style sheet for login pages.</li>
<li>Change the URL and TITLE of the header link.</li>
<li>Add specific messages to the different login pages (Login, Registration, Forgot Password)</li>
<li>Change various error messages on login and registration pages.</li>
</ul>

DBD Login Style

Add style to your login page!! This plugin enables you to specify a style sheet to be used on the login page.

Smithers Login vs DBD Login Style