Atolm is a new dark GTK theme created by SkiesOfAzel (who is also behind the very popular Orta GTK theme) in collaboration with MonkeyMagico who's mockups were the inspiration for this new theme.
To use Atolm, you'll need the Murrine, Pixbuf and Equinox GTK engines. The Equinox GTK engine comes with an Ubuntu PPA so to install it, use the following commands:
sudo add-apt-repository ppa:tiheum/equinox sudo apt-get update sudo apt-get install gtk2-engines-equinox
Then download Atolm, extract the downloaded .zip archive and you'll have a .tar.gz which you can drag'n'drop onto the Appearance Preferences 'Themes' tab to install the theme.
SkiesOfAzel recommends the Aworken icons for this theme, but I would personally recommend F-Dark Faenza. If you know other icon themes that look good with Atolm (or any other dark themes), let us know in the comments!
Thanks to SkiesOfAzel for the tip | Screenshot via Atolm DeviantArt page.