While the basic scenarios are white on black and black on white, most programmers find more varied syntax highlighting useful.
What advantages do you find from a general setup? (E.g. "a dark background allows...")
What specific tweaks do you find most helpful? (E.g. "slightly off-white works to...", or "highlighting quote marks and escapes, like \n, differently shows...")
One answer per person, please; list multiple points as part of your one response, if needed.