Was watching some highlights recently and thought this would be fun.
Aus vs SA, Edgbaston, 1999 WC
Warne on fire, has clean-bowled Gibbs and Kirsten after a great start by the Saffers. Cronje nicks out to slip and is given but wait, he's referred it and the 'catch' is found to have gone off his foot. The decision is reversed and I reckon South Africa would have won.
Aus vs WI, 4th Test, Adelaide, 1993
I bet everyone here old enough to remember the game thinks of the McDermott dismissal for this one. Well you'd be wrong because if DRS was around at the time, it would never have gotten that far; Billy was nailed on the back-foot by Walsh early in his innings and inexplicably given not. Terrible decision but had it been correctly given, WI would have won by 30-odd runs from memory.
Aus vs Eng, 2nd Test, Edgbaston (again), 2005
A 2-run loss would have been about a 60-run loss if Kasper had been correctly given leg-before early in his knock.