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!

ООО «ЭйВиДи-системы»

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 theme WordPress and this plugin takes over.
Note that you should use a transparent background on the PNG custom logo, crop it tightly (no padding pixels) and use a width of exactly and min 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.

SK-Elib

Customize the logo on the WP login screen. Using a custom logo from your WP theme. CSS is automatic!

Login Logo vs SK-Elib