I'm working on different systems and every system uses different fonts in their editor. I like to introduce some fonts in Linux and it might help you to find your favorite. This is not an article about WordPress directly, but many of us using an editor for the most time, while developing with WordPress.
A similar article, more for Windows user, written by Jeff, can be found in his post Revisiting Programming Fonts.
As an example I created a little script, which doesn't do anything, but it demonstrate the fonts nicely. I'm using the IDE Aptana, it's very nice to work with; as of right now version 2.*; the coming version 3 offers many new features and can be tested as beta.
I used for all fonts the same size and also the screenshots are the same.
While I'm very happy with Droid on the system, I'm using Monospace in my editor. In Windows I'm using Consolas, 11 points regular.
Monospace 11 Regular
Andale mono 11 Regular
Courier New 11 Regular
Verdana 11 Regular
Inconsolata 11 Regular
Free mono 11 Regular
Droid 11 Regular
DejaVu 11 Regular