When Hingis hits that shot, you just go "What the...? Where did that come from?" I remember very specifically the 1997 US Open Final, she hit a stunning one to out-maneuver Venus Williams and it was the highlight shot of the match for Hingis.
In addition, Serena Williams on clay circa 2002 (?) had a highly dangerous crosscourt short angle backhand, but I don't recall the level of topspin on it. That was the shot she won the French with, though.