Hybrid-Man-of-Steel is a superb dark and red GTK3 theme that you can use with Unity and Gnome Shell under Ubuntu 11.10/12.04. In this tutorial we will help you install and enable Hybrid-Man-of-Steel using few terminal commands. Here is a screenshot of this theme under Ubuntu Oneiric (Unity):
I used with this theme the Area icon theme, you can find here how to install it.
Open the terminal (Ctrl+Alt+T) and run the following commands:
unzip Hybrid-Man-of-Steel-gtk3.zip -d ~/.themes
gsettings set org.gnome.desktop.interface gtk-theme 'Hybrid-Man-of-Steel-gtk3'
gconftool-2 --set --type string /apps/metacity/general/theme 'Hybrid-Man-of-Steel-gtk3'
Credit for this theme goes here.