Lithium is a sleek and stylish dark theme for Gnome.
Several gorgeous and subtle features really enhance this theme.
The currently highlighted window lights up with an orange glow on the taskbar, and hovering over a window button creates a cold steely blue glow over it. Simple yet incredibly effective little tweaks.
Using the glowy Ubuntu icon from HumanLoginIcon theme set included in Karmic can enhance the theme, further.
Download Lithium @ gnome-look.org