I took the theme from ArduOpen and modified it a bit, adding back the default icons/tabs and tweaking some colors. I figured I'd share it in case anyone else was having a hard time staring at the bright default IDE and couldn't find any good dark alternatives. Props to the ArduOpen team for their great color choices.

http://www.ledseq.com/downloads/arduino_theme.zip

EDIT: To install a theme (at least on Windows), rename the "theme" folder in your /lib folder to something else like "theme_original" and then copy the theme folder in the zip I provided into /lib instead. Restart the IDE.