Kalahari is a pack of elegant icons for Gnome-based systems like Ubuntu. This icon theme is inspired by the Faenza icon theme and is compatible with Unity and Gnome Shell. Here is a screenshot of it Under Ubuntu Unity:
You can install it under Ubuntu 12.04/11.10 using the following PPA:
sudo add-apt-repository ppa:upubuntu-com/themes
sudo apt-get update
sudo apt-get install kalahari
You can either use Gnome Tweak Tool to enable Kalahari, or use this command from the terminal:
gsettings set org.gnome.desktop.interface icon-theme 'kalahari'
Credits for this icon theme go here.