diablue

Plugin allows admin to upload custom logo for WordPress login page.
After activating the plugin, follow these steps:
<ol>
<li>Go to Settings -> Custom Login Logo</li>
<li>Click “Choose Image”</li>
<li>Select or upload your logo</li>
<li>Click Save Changes</li>
<li>Refresh the login page to see the new logo</li>
</ol>

Diablue Login Customizer

Easily add a custom logo to your WordPress login page using the built-in media uploader. Change WordPress login logo from admin panel.

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.

Diablue Login Customizer vs Simple Login Screen Customizer