I'm a bit of a fan of orcs, and play them a lot. Despite them not being my *favourite* race (I like humans best), or a particularly powerful race (drakelings and dark elves for me, depending on class), I still probably play about 35% of my adom games as orcs...
I can't really get behind the notion that they need a buff or more identity. I think find weakness already makes the hugely different to dwarfs and trolls.
However, if one were necessary, how about giving them an increased crit chance or damage based on their missing hitpoints?
(An even more fun mechanic would be for them to get a 'bloodlust' damage bonus based on monsters killed, divided by time played(turns, gametime, real time, whatever). That, provided the damage boost was never outrageous, would make them a VERY interesting race to play)