Cupped hand on the ear, anything to the eyes, windpipe, etc.
I used to teach the rape-defense classes and we'd tell them the highheel stomp to the instep. I never really believed it until I dropped a heavy wooden pallet on my instep, wearing a workboot, and limped for two weeks.
My friend once had a school toughguy up in his face, you know, the chest to chest, nose to nose thing. This was a big dude, and Joesneak-attacked him by suddenly pushing him sideways, so his weight was more on one foot, then did this little inside kick to the ankle, and the guy ended up spraining it. He just rocked him up on that foot and stomped it kinda quick.
Never done it fighting, but rolling and messing around I had my buddy pinned in a crossbody position, and just for fun, I held his arm down and elbowed him lightly where the biceps and triceps meet just a couple inches above the elbow. It hurt him like crazy, like really hurt him, and I felt like a jerk.
Once in a real match I took a guys back, but could only get one hook in. I put my left elbow between his shoulders and hooked the opposite tricep in my hand, thinking of the armlock, and he was bucking me off his back to the left. For just a minute his right side ribs were open and the range was perfect, so I elbowed him with the right elbow in the kidney. I really thumped him, and I think it won me the match, because he acted hurt and I got a choke on him a second later.
That little hollow above the sternum is really bad, because it makes you cough and lose breath. I punched a kid during wrestling practice because he kept digging a thumb in there, and almost got kicked off.
I still think the collarbone is underrated. I've seen a lot of MMA fights where the guy is in guard or crossbody or side control and trying to elbow the head or face, but the distance is wrong, he's to close or he's too high, but where he could easily land a very powerful shot with the point of the elbow on the collarbone.
I f you can take out legs with thigh-kicks I think other muscles could be taken out, too. I emember a couple of guys elbowing the thigh.