I use Emacs. A lot.
There are two that I flip back and forth between every so often. Currently I’m using this brown-ish theme:
When I get bored with that one, I use this neon theme:
That neon one might look familiar because it’s based on the Monokai theme for TextMate. I based mine on this port to Emacs and then added things like settings for egg-mode and org-mode since I use those modes a lot.