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.

sureshdsk

Use wp-login customizer to change wordpress logo,background image and Powered by wordpress.org link on your wordpress login page. 
More information: <a href="http://www.cloudwark.in/wp-login-customizer-wordpress-plugin" rel="nofollow ugc">wp-login customizer</a>
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wp-login customizer

Customize wordpress logo,background image and Powered by wordpress.org link on wordpress login page.

Simple Login Screen Customizer vs wp-login customizer