Some of the races in the advanced race guide from pathfinder probably count. Try playing a Tiefling or a Strix. Or maybe ask your GM what your campaign's primary enemy will be. If you learn that there are a whole lot of Orcs to be slaughtered, see if you can play an Orc. I mean, this depends on what you want to get out of being a "monster." If you're talking having to deal with the reluctance of being abnormal, and your friends/carreer/adventuring life putting you in conflict with your nature and past, then this would work. If you want to be a monster in the sense that you're Chaotic Evil and rampaging around, perhaps try something like a Centaur Barbarian. I can't remember if it was D&D 3.5 or Pathfinder, but in one of them, Centaurs get +8 Strength, so a properly built one could get a strength mod pretty close to 10 straight off the bat, and as a Barbarian, you don't have to be civilized, literate, or even able to speak.
