Not the biggest ever, but Kate Winslet winning for the Reader was a bit of a 'crap, she's been nominated 6 times for better films we better hurry and give it to her'. Her performance in Revolutionary Road in the same year was far superior. BUT she should have won for Eternal Sunshine of the Spotless Mind. She was amazing in that.
I think she was amazing in all three.
(Big Kate fan)
I was pretty shocked to see Denzel Washington win for 'Training Day', but that's mainly because I thought Russel Crowe had it in the bag.