Carlos Zarate comes to mind. He got wild sometimes, and his best defense was a good offense. But he put together great combinations with hellacious body punching, and was so fun to watch.
Julian Jackson couldn't outbox top contenders, so his only chance was to knock guys out. As far as reactions from fighters when they get hit, he's very high up. I'm glad someone mentioned Bennie Briscoe. He had the same problem in that his only real chance was to KO guys. He gave Monzon hell for a while with sheet tenacity. Foster had an awesome jab and great reach going for him, and guys looked like they were dead if he connected. He fought a guy from Puerto Rico once and I thought that he honestly killed the dude. The ref continued the count to ten and they had to pry the mouthpiece out.
David Tua comes to mind quickly as well.
