I really love writing in a decent mono-spaced, non-serif, font. From hacking in the terminal to writing Markdown in nvAlt, having a nice font seems to make things just a little nicer.
There's a great article which I've just read which gives you the chance to view the best programming fonts, including a sample of code.
Source Code Pro has edged ahead (yes, there's a vote!) but I'm glad to see a few new mono-spaced friends I can add to my list.