HueTheSpa Openbox theme, bundled with a "matching" GTK2 theme that uses the Rezlooks engine. (1)
It's got some green, it's got some brown, it's got some grey. Nothing shiny, flashy, gradienty or globby. Very flat, very simple, very fast. Because that's the way I like it.
Color selection shamelessly stolen from the "Subtlety of Hue the Spa" arrangement, found on kuler.adobe.com. (2)