GRiM Style Theme for Windows 7 (Tested on RTM build 7600 x64 only). I do like the start menu glowing effect and the crystal transparency.
If you have no idea how to apply themes in Windows 7, look at this first:
If you don't know how to replace system files when applying a nice theme, here is an article you might need:
www.vista123.net, easily tweak and customize your Windows Vista.