As programmers we probably spend most of the day staring at our favorite editor (mine is Homesite... though maybe Dreamweaver 8 will finally break me) so we might as well make our experience as comfortable as possible. Changing your editor font can make a huge difference. This site lists many of the best monospace / fixed width fonts with screen shots of what they look like. If you've got a favorite, let me know.

For me, the hands down favorite is Andale Mono. It used to ship with the windows font pack, but you have to hunt around for it now. I pretty much carry it from job to job on cd.

Something else that is worth a gander is how your fonts are rendered to the display. Win32 has a technology called ClearType (their name for sub-pixel font rendering) and there is a newer-ish control panel wizard to tune this for LCDs:

http://www.microsoft.com/windowsxp/downloads/powertoys/xppowertoys.mspx

or you can use the old web-app to tune ClearType:
http://www.microsoft.com/typography/cleartype/tuner/Step1.aspx

The configuration process is just like a vision exam: which looks better... this or that one? It can even accomidate weird LCDs such as the old 18" Dell BGR (instead of RGB.)

Other operating systems have this technology as well... apple terms their version font smoothing and even kde running on GNU/Linux distros have a sub-pixel rendering option.

Steve Gibson has a nice write-up on Sub-Pixel tech.
http://grc.com/cleartype.htm

Monaco by far.