Mark Jaquith

This plugin allows you to customize the logo on the WordPress login screen. There is zero configuration. You just drop the logo file into your WordPress content directory, named <code>login-logo.png</code> and this plugin takes over.
Note that you should use a transparent background on the PNG image, crop it tightly (no padding pixels) and use a width of exactly 312 pixels for best results. Wider images will be downscaled in modern browsers, but it isn’t recommended to rely on that.
This plugin also works in the <code>mu-plugins</code> directory.

Login Logo

Customize the logo on the WP login screen by simply dropping a file named login-logo.png into your WP content directory. CSS is automatic!

Haris

Astahub

A fine designed and unique WordPress login page style that includes some customizations, also comes with login theme selector. Yaaaay!
Features :
<ul>
<li>Nice and well designed login style</li>
<li>Responsive design</li>
<li>Customizable login title</li>
<li>Customizable login logo</li>
<li>Customizable login message</li>
<li>Comes with 4 awesome login themes</li>
</ul>
Usage Instruction :
<ol>
<li>Install the plugin</li>
<li>Open the settings page on Appearance -> Login Screen</li>
<li>Change the plugin options then save it</li>
</ol>

Custom Login Screen

An unique and customizable WordPress login screen.

Login Logo vs Custom Login Screen