AJ Troxell

With the Custom Login Page, you can change the background image of your login page, the background image/colo of your login form div, the main logo image of your login page, and add custom CSS. 
All through a simple interface. Remember to view the Help tab at the top of the settings page for the plugin.

Custom Login Page

Wordpress Custom Login Page allows you to change the background image, logo, form div attributes, and custom css of you Wordpress login page.

António Campos

With this plugin you can easily choose one image from your gallery and use it as logo in your wp-login.php

AC Change Login Image

This plugin changes the image in the login page (wp-login.php), you can choose any image from your gallery and use it as login logo.

Custom Login Page vs AC Change Login Image