A lovely GTK 3.0 theme and wallpaper set for MATE and Gnome Shell.
I have recently installed the Gnome Shell desktop on Linux Mint 14 and I have found a nice theme set for that desktop.
Type this command to install the Bluebird theme and some nice wallpapers.
sudo apt-get install shimmer-themes shimmer-wallpapers
This installs the GTK theme engine, some wallpapers and a nice Metacity theme that is very attractive indeed.