Half-left has designed yet another great theme for Gnome Shell. His latest theme is based on the look of Ubuntu 12.04 Precise Pangolin and it looks really beautiful.
Download Ubuntu Precise Pangolin Gnome Shell Theme
Use User Theme Extension and Gnome Tweak Tool to switch Gnome Shell themes. Gnome Tweak Tool can be installed from Ubuntu Software Center. User Theme extension can be installed by running commands below:
sudo add-apt-repository ppa:satyajit-happy/themes
sudo apt-get update
sudo apt-get install gnome-shell-extensions