The Windows 8 login screen that is used in the leaked M3 build and possibly in Windows 8 beta builds was leaked by withinwindows:
Very minimalistic design, I like it already.
The login screen background is based on one of the default Windows 7 wallpaper. If you haven’t spotted it on your Windows 7 PC yet, here’s the wallpaper:
I’m wondering if the same artist who created the “crazy” Windows 7 wallpapers is also going to create some of the new Windows 8 default wallpapers. Hopefully! I very much liked some of them.