Ubuntu's Ambiance and Radiance themes with proper scrollbars and fixes for the Nemo file manager.
CSS code for the scrollbars was adapted and modified from the Greybird theme.
I recommend setting the environment variable GTK_OVERLAY_SCROLLING=0 (example: export GTK_OVERLAY_SCROLLING=0) in your .profile file for best results.
These themes were only tested in the Unity desktop environment, but should work with any GTK-based desktop environment.