allilevine

This plugin adds an options page (Settings > Login Screen) that allows you to customize the WordPress Login Screen (wp-login.php). You can:
<ul>
<li>Upload a custom logo (it will be resized to fit if necessary)</li>
<li>Choose a link color</li>
<li>Choose a link rollover color (defaults to a darker shade of the link color)</li>
<li>Choose a button color (defaults to a button version of the link color)</li>
</ul>
The plugin also links the new logo to your site URL.

Simple Login Screen Customizer

Good

Choose a logo and link color for the login screen.  The plugin will do the rest.

Scott DeLuzio

AMP-MODE

WordPress Login Logo Editor is a plugin that easily lets you edit the form and logo shown when logging into your WordPress site. WordPress Login Logo Editor allows you to edit:
<ul>
<li>The image above the login form on your WordPress site.</li>
<li>The URL that a user gets directed to when the logo is clicked. By default you are directed to http://wordpress.org.</li>
<li>The title text that appears when your mouse hovers over the login logo. By default this text says Powered by WordPress.</li>
<li>Style the login window with custom CSS.</li>
</ul>

Login Logo Editor

Easily lets you edit the form and logo shown when logging into your WordPress site.

Simple Login Screen Customizer vs Login Logo Editor