Well, it’s no wonder Mac users like Monaco more than Windows users, it does look significantly better when rendered on a Mac than on Windows. When talking about anti-aliased fonts in larger sizes though, sure there are better alternatives. Jacob Rus said it, Monaco really dows look its best bitmapped and in 9 or 10pt (and 9pt Monaco was actually the OS font for icon labels in the Finder, later on upped to 10pt). But I think you’d be hardpressed to find a font that does a better job than Monaco of looking good (on the Mac at least) both as a small bitmap and as a scalable, anti-aliased programming font.
Take a look at this:
Bitmapped 9pt Monaco. Looks a lot like that ProFont some people rave about here, if you ask me.
For me personally though, I’ll stick with Courier. The serifs really do ease legibility, in my opinion - and it saves vertical space.