This is just a simple mod of Dave87's Sunset GDM that can be found here...
All I really changed was the background and I removed the transparent boxes.
I love his layout but wanted something in black, (or at least something dark).
**** 24 Nov 2008 - UPDATE ****
Added wide-screen version
Standard version should look good up to 1600x1200
Wide-screen version should look good up to 2560x1600
Also added versions of each with the login box more centered.
Both standard and wide screen are in one tar.gz. Just delete the one you don't want to keep from inside login manager after you install.
***Added mirror site. This is my personal file server and is not always available but if it is you won't need to wait to download.