Consolas is my favorite monospace font. It’s a good programmer’s font because it exaggerates the differences between some characters that may easily be confused. It ships with Visual Studio and with many other Microsoft products. See this post for examples.
I recently found out about Inconsolata, a free font similar to Consolas. Inconsolata is part of the OFL font collection from SIL International.

Another interesting font from SIL is Andika, mentioned previously here. The Andika home page describes this font as follows.
Andika is a sans serif, Unicode-compliant font designed especially for literacy use, taking into account the needs of beginning readers. The focus is on clear, easy-to-perceive letterforms that will not be readily confused with one another.
Related posts:
Better R console fonts
Adding fonts to the PowerShell console
Comic Sans and dyslexia

{ 4 comments… read them below or add one }
Daniel Jimenez 09.21.09 at 12:34
I’ve always been a fan of the RedHat Liberation fonts: https://www.redhat.com/promo/fonts/ (follow the Fedora Hosted link in paragraph 2).
Their biggest weakness is covering only ~25% of the mathematical glyphs – gosh those are useful.
Wedge 09.21.09 at 12:57
Droid Sans Mono is also a great free, true type, monospaced font: http://damieng.com/blog/2007/11/14/droid-sans-mono-great-coding-font
John Moeller 09.21.09 at 15:49
Inconsolata is lovely and quite crisp, thanks for the recommendation. It’s great for xterm, and it’s available in the Ubuntu repository, for those interested.
Karl Ove Hufthammer 09.23.09 at 09:04
I have used DejaVu Sans Mono since it became available, and I think it’s an excellent monospace programmer’s font. All the commonly confused characters such as oO0Ø and 1l|¦ look very different from each other, the font looks great at small font sizes, and it has extensive Unicode coverage.