I recently bought these 2 HTD M3 belts (http://www.optibelt.de/fileadmin/bilder/produkte/industrie/Zahnriemen/PDFs/Omega.pdf)
The exact name is: HTD 945 3M 9 OPTIBELT OMEGA
They are similar to GT3 belts (or the same?), I think that's just what they're called here in Austria!
Both belts are continuous 945mm and 9mm wide, so they fit for a standard Prusa Mendel! (And other applications I suppose)
I also bought 2 Aluminum pulleys that fit the belts, called ZRS 16-3M-9, so 16 teeth, for belts up to 10mm wide and predrilled with 4mm!
One of the pulleys is damaged, tried to drill a straight hole and kind of ruined it in the process, might be fixable with a good lathe, not sure (there's a 5mm hole in it which is not centric)! The second pulley + the 2 belts are brandnew! (That's the reason I am selling them again, because I can't use them without having acces to a lathe)