I recently discovered the M+ fonts (http://mplus-fonts.sourceforge.jp/mplus-outline-fonts/design...). "M+ 1m" is a very nice condensed monospace font that works well on my 13" MacBook Pro's small screen. However, there seems to be too much vertical space between lines, and it tends to be blurry at smaller font sizes, so I wouldn't recommend it 100%.
Mathematica can be really finicky regarding fonts in graphics when it comes to what it thinks of as "math" symbols. This has to do with the way that it typesets equations- most fonts won't have glyphs for integral symbols, for example. Let's say that for some odd reason you wanted to typeset an equation in Zapfino. Mathematica will be happy to do this, but since Zapfino lacks integral signs and numerous other mathematical symbols, Mathematica will helpfully substitute glyphs from its own built-in fonts "as needed."
Unfortunately, it can be overzealous about this- its definition of "as needed" is awfully broad. I recently had a seriously annoying problem involving a graph I was trying to export- I'd set the graph up using Optima, but the graph's title included parentheses and a percentage sign. It all looked fine on the screen, but upon exporting it I found that the (, ), and % were all in the wrong font, since Mathematica decided that those were math symbols and as such needed to be substituted out for glyphs from another font. Turns out there's a (well-hidden and poorly-documented) way to manually override this font-embedding behavior- if any Mathematica users out there are interested, drop me an email.
Style["( . ) ( . ) ", 60, FontFamily -> "Comic Sans MS", PrivateFontOptions -> {"OperatorSubstitution" -> False}]
Supposedly, the newest version of MMA has improved its font embedding behavior such that it all should "just work," but I haven't had a chance to test it out yet.