• Monospaced.
• Legible in small font sizes on screen and print. It needs to be well hinted, yet still be an OpenType font, not just pure bitmap so that it can be used in HTML and documentation as well.
• The letters uvw wW gq9 2z 5s il17|!j oO08¤ ;:,‚„. ‘`'’“ "” m nn rn {[()]} all must be very distinct, even if you have to distort the glyphs. The punctuation should be oversized for clarity.
• Rich character set at least including the accented letters é Ç, (for internationalisation) and currency symbol ¤.
• The font should not be needlessly horizontally or vertically elongated. Every pixel of screen real estate is valuable to a programmer. You want to pack as much as possible on the screen without it giving you a headache to look at.

The following fonts are the best programmer fonts I have found so far. I consider only fonts that are scalable. The best are near the top.

• Bitstream Vera Sans Mono Includes mono and proportional variants, oblique and bold. Created by Bitstream. Looks wretched without anti-aliasing. Looks superb with it. All characters have easily distinguished shapes. The w and m don’t fill in with small font sizes. You can even read it at 8 points. Free. You might want to have some other font in your back pocket to use where anti-aliasing is not available. If you use this font is a web page, others may not have it, and even if they download it, they may not have anti-aliasing. If I were designing the font, I would make the m more open, by reducing the length of the middle stem, so it would look like an ε rotated. The psychological feel of the font is relaxation and calm. I can’t explain how it creates that illusion. This is what I am using myself, at least for now. Bitstream Vera Sans Mono looks like this:

  

• Pragmata: elegant, clear, Euro-looking, but costs €90.00 EUR . Comes in Mac and PC versions. Reminds me of the fonts used by Burroughs in the 1980s. Astoundingly clear at 9 points. Here is what it looks like. The letters are all beautifully distinct and compact. Pramata looks like this:

  

  The font’s designer Fabrizio Schiavi kindly prepared the above sample for me using my FontShower Applet. His font does not actually support the accented g character, so he substituted one. That is why it looks different from all the other characters. The only weakness is 8/0 are a bit too similar. I wonder how you could fix that perhaps clearing the centre of the 0 and making it shorter and putting a diagonal ear in the upper left and lower right corner, like a slashed 0, but with the center open. Perhaps just as small dot in the middle, or perhaps the way Vera does it with a horizontal bar across only the right half of the 0.

• Andale Mono: characters are very distinct.$30.00 USD . You can study this font without buying it by using the font sample generator available at the link. Its weakness are the various quotes. They are delicate and hard to tell apart except at quite large sizes. I wish type designers would make punctuation bigger and more distinct in small point sizes, and make them less obtrusive and deformed in the larger sizes. Andale Mono looks like this:

  

• TheSansMono: A quite beautiful font. This comes in 3 widths, 8 weights and italics. The catch is you have to buy each variant as a separate font. If you get just the four basics, it will cost you a whopping $98.00 USD . There are related proportional fonts too. theSansMono looks like this:

  

• Lucida Console: comes free with Vista. Somewhat wasteful of screen real estate. Looks very sharp at slightly larger font sizes, but somewhat flea-bitten at small ones. Lucida Console looks like this:

  

• Lucida Sans Typewriter: comes free with Java. Similar to Lucida Console, but has taller caps and bigger digits. Lucida Sans Typewriter looks like this:

  

• Consolas Comes with Vista. Quite nice looking, especially on an LCD at high res. The dots over the i’s in italic are oddly extremely displaced to the right. The i1l are not quite as distinct as I would like. The braces are look a bit too much like vertical bars {|}. The letters touch so that rn and nn look too much like m. Consolas looks like this:

  

• Proggy Clean slashed 0: PostScript, TrueType, X-Windows or Mac format. A bit ratty looking. Comes in many variations. free. Free. Proggy Clean looks like this:

  

• Oloron: automatically grossly bolds the punctuation. TrueType.$20.00 USD Oloron looks like this:

  

• Anonymous: this is a bit map font available in 8, 9, 10 and 11 points. The letters look unusually distinctive and it is aesthetically pleasing as well. Free. Anonymous looks like this:

  

• DPCustomMono2: is a true proofreading font. However, it has some flaws in the metrics that cause some apps to render insanely every once in a while. Good for viewing, but not for editing. It absolutely must have anti-aliasing to be tolerable. Free. DPCustomMono2 looks like this: