Alpha-1 is a set of dark icons for the Gnome desktop environment. In this tutorial we will help you install and enable Alpha-1 in Ubuntu 11.10/12.04. We have previously covered many icon themes, you can check them all here.
cd /tmp && wget -O alpha.zip goo.gl/ymbWP
unzip alpha.zip && tar jxvf /tmp/Alpha-1/Alpha-1.tar.bz2 -C ~/.icons
gsettings set org.gnome.desktop.interface icon-theme 'Alpha-1'