Good topic. Nothing like the sound of a good leg kick.
Cro Cop is the current king of the leg kicks. If you take a bat, and swing it at someone's leg, then you still wouldn't duplicate a CC leg kick. Incredibly hard, menacing leg kicks. Such malice thrown in them, and watching Yoshida crumble from them proved how sickening they are. Hell, and Yoshida has pants on.
Bas had some mean leg kicks. Those damn Pancrase boots couldn't block the force of them. In his debut fight, he delivers such a nasty leg kick. I'm sort of biased here, and I think Bas could chew gum better than anyone.
Pedro Rizzo had some awesome leg kicks. He was too much of a mental midget, but he did enough to get his point accross. Incredibly hard and accurate. Watching Dan Severn go from "I'm sort of screwed here...*KICK*...I'M SO DEAD!" showed how nasty Rizzo can be with his leg kicks.