GnomishDark is a clean dark theme for GTK3, based on Adwaita (provided by gnome-themes-standard), plus a matching GNOME-Shell theme.
The package also includes a GTK2 theme, that depends on the latest Murrine engine and makes GTK2 windows fairly similar to GTK3 ones. If you don't want to install Murrine anymore, you could replace the folder 'gtk-2.0' with that of Adwaita but you'll lose the above-mentioned similarity.
Notes:
1) For now, the theme depends on GTK+-3.2, gnome-themes-standard-3.2.X and gnome-shell-3.2.X. With later versions of these packages, the theme might not look as in the screenshot. In that case, I'd update it as soon as possible.
2) Like it's the case with other dark themes, there are readability issues in LibreOffice and also in webpage combos when seen with some browsers. The first issue can be fixed by changing "OOO > Tools > Options > LibreOffice > Appearance > Document background" to white after disabling automatic detection of high contrast in Accessibility.
3) The panel font is Bitstream Charter, provided by xfonts-scalable in Debian based systems, but it's not necessary.
4) In VirtualBox, text shadows may be rendered wrongly. In that case, you could remove all lines starting with "text-shadow:" from "gnome-shell.css".
How to install?
http://news.softpedia.com/news/How-to-Install-GNOME-Themes-in-Ubuntu-11-10-231213.shtml
About GNOME:
GNOME is an international effort to build a complete desktop environment—the graphical user interface which sits on top of a computer operating system—entirely from free software. This goal includes creating software development frameworks, selecting application software for the desktop, and working on the programs which manage application launching, file handling, and window and task management.
GNOME is part of the GNU Project and can be used with various Unix-like operating systems, most notably Linux, and as part of Java Desktop System in Solaris.
The name originally stood for GNU Network Object Model Environment, though this acronym is deprecated. The GNOME project puts heavy emphasis on simplicity, usability, and making things “just work”.
Product's homepage
Requirements:
· GTK+
· GNOME
What's New in This Release: [ read full changelog ]
· Fixes.
· A better workaround for Epiphany.