See what I was saying about him having a whiplash motion on the forehand?
I can't think of anybody else offhand that has that kind of exagerrated whiplash action on the forehand. Initially I was thinking Rios, but after watching some clips, Rios' was more of a body whip. A better example is Safin. Safin definitely had that whiplash action on his forehand, though not quite as exagerrated as what you see with Williams.