There are many kinds of nerds; this one's for the font nerds out there: My Favorite Font. It's an article on Slate in which authors run down their favorite fonts. "Courier" seems to be the runaway favorite, but "Palatino", "Century Schoolbook" and "Hoefler" make appearances.
Personally, I'd probably have to go with "Courier"; it brings back happy memories of writing my first short stories on the typewriter I borrowed from my dad. I also find it a very readable font, particularly when I print out copies of my reviews and columns for proof reading, and used it when I my novel during NaNoWriMo last year. "Lucida Grande" would be my second runner up; it's the default font for BBedit, and I've spent far too many hours coding in it.