The monospaced fonts that come with your Windows box (like Courier New) aren't particularly good at distinguishing capital O's from zeroes and semicolons from colons, and that can make debugging more difficult.
Andale Mono slashes 0's, so it's very helpful on that score. It was once freely available from Microsoft, but is now discontinued. There are undoubtedly some illicitly-available copies rattling around somewhere.
My preferred font now is Bitstream Vera Sans Mono, which does a better job of sorting out :'s from ;'s.
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