Deviantart user Half-left has designed a great theme for Gnome Shell. His latest theme is based on the look of Ubuntu 12.04 Precise Pangolin Ambiance theme and is an absolute eyecandy.

 To download the Precise Pangolin Ambiance theme for gnome shell click here.

Please Make sure you have user-theme-extension installed. To download gnome theme extension use the following commands.
  • $ sudo add-apt-repository ppa:satyajit-happy/themes
  • $ sudo apt-get update
  • $ sudo apt-get install gnome-shell-extensions

Now Load the GNOME Tweak Tool and go to Shell Extensions and click the "Use Theme Extension" switch. Now go to "Theme" and click the Shell Theme box and locate your theme zip. Now you can select the theme in the dropdown box.

Enjoy! :)