On my Mac I have "Courier" and "Courier New". I use Monaco and Lucida Sans Typewriter.
I use the freeware Anonymous as my monospace typeface of choice. There are a few characters that looked strange to me at first, but I find it quite readable and (most importantly) it's creator actually bothered to differentiate 1, I, and l as well as 0 and O. <http://www.ms-studio.com/FontSales/anonymous.html> -- Jeremy Weathers Sony-Ericsson: We put the "slow" in "Damn, this crappy phone is slow!" - Wil Shipley
