Customize OS X's Login Screen with Any Logo You Want
The login screen on your Mac is perfectly functional as it is, but if you want to spice it up a little bit, blogger Jacob Salmela shows you how to customize the login screen with a logo of your choosing.
If you don't want to install a whole program just for a simple tweak it's easy to do manually. All you need is a PNG that's 428 X 248. Then, you'll need to save it as four different files.
You need four copies of this file, and they need to be named:
Once they are named correctly, just drag them into the following path:
and then choose to replace all of them.
That's it, log out, and you should see your new logo. Head over to Salmela's site for a few sample images and instructions for making your own.