In the past few months, several folks have weighed in on their favorite fonts—Cory Doctorow waxed poetic about Droid Sans Mono while James Duncan Davidson professed his love for Bitstream Vera Sans Mono (His blog died, so the link is to a post about his post).
I've tried a lot of different fonts over the years, but I always come back to the most boring and plain screen font ever. It doesn't even have a real name--I know it only as "9x15" and it comes with X11. It's pretty much the only font I've ever coded in, and I've got my emacsen all hard-wired to use it, on both Mac and Linux. Click on the image below to see the full-size version (Stupid Blogger image upload insists on resizing my images).
I'd love to find an actual vector font that looks just like 9x15, but I've yet to find one, despite quite a bit of hunting.