Composing Mathematics Papers

I was just wondering if anyone had recommendations for programs/document editors that are good for putting together professional-looking formulas and papers? Free and Windows-compatible is always nice, but "free" non-windows apps would work as well. A quick googling led to nothing of use.

Thanks guys.

>>5
Well, if you fuss around enough with the fonts and such, I'm sure you could make something in Word that looks just as good.

That's not the point, though.  The bottom line is Latex is just a million times easier once you know how to use it.  You could spend 15 minutes in Word setting up some triple integral or whatever that would take 45 seconds in latex.