From what i've seen three of the best ever were Marco Pantani's 2 victories up l'Alpe d'Huez in 95 and 97 and Bjarne Riis on the road to Lourdes in 96.
Pantani was poetry in motion on a mountain stage whilst Riis dropped from the front of a group of about 8, including 5 time defending champion Indurain, down the line, looked at each in their eyes and then launched a stunning attack. Of course, it's since come out that he was on drugs but at the time the theatre of the move was stunning.