Real rappers are ones who represent themselves truthfully to the people, through there lyrical content and style, don't pretend to be something they aint, spit shit that they themselves believe and that many people can feel plus they don't rap shit they don't believe just fo a buck.
This doesn't mean you can't be commercial (2pac was as real as it gets) but it does mean you can't rep shit you didn't do or don't really believe.
Real rappers out there are the wu in particular the gza, jedi mind, nas, gangstarr, pac, mos def, kweli, de la, etc.
That's a tough question man. So fucking subjective.