Sam Alvey is a good example to me. He looks so slow and plodding, and certainly doesn't have an impressive physique by MMA standards, yet he hurts almost everyone he lands on.
Much longer ago than I really care to think about, I was watching a boxing match. Two heavyweights, one had they other backed against the ropes and was leaning on him. The dude against the ropes threw a short left hook that flatlined the other guy. I'd give a name if I could dredge it up, or even had something to go by to Google. It was back when ESPN and USA both had weekly boxing shows. I remember watching the replay and thinking, "How the fuck did he generate any power at all with that shot?"