Moka is a Gnome Shell theme that uses simple geometry & basic colouring.
Ranked in these QuestionsQuestion Ranking
Pro Wide support
Pro Several distro specific instruction to download
Moka offers suers easy to follow instructions to download including PPA's for Ubuntu based distros and Fedora specific instructions to install its repo.
Con Does not work on older version of Gnome Shell
Moka does not work on Ubuntu 12.04 nor will it work on Debian Wheezy as they both use old version of Gnome Shell.