Under XP, there are plenty of alternatives - currently I use the Consolas font - but fonts render differently under OS X. So I spent some time getting this right on my MacBook with a 1200 x 800 display. I have found that spacing between lines is very important to me
This is the default Monaco as chosen by Eclipse. It is a bit too small for using on a 13" Mac.
Monaco at size 13. This is actually quite nice with proper spacing and large, readable characters and may be perfectly fine for most. Unfortunately I don't like the asymmetry in the characters (they all look like they were pushed on the upper left corner), but it is ok.
This is size 13 of the Liberation Mono fonts from Red Hat (which were designed to have the same physical size as the fonts Microsoft provides), and which is really nice. I have used it for a while and it is fine.
The Inconsolatas font at size 14. This is my personal favorite - fine spacing and kerning, not too black letters but not too thin either. The author was inspired by the Consolas font and has done a great work.
