Ronaldinho at the Bernabeu seems like an obvious choice. It was before the era of superhumans like Messi where doing something like that left you genuinely awestruck.
Neuer at the Westfalen in his final season for Schalke was amazing. I mean Joe Hart was impressive and all but he mostly dealt with shots outside the area. I'll never forget Neuer rushing out against Lewandowski saving the ball with his ribs before sprinting 30 yards and catching the ball when Götze crossed it. Didn't believe it was happening when I watched it. Had some insane saves where he frankly had no right to get a hand to the ball.
And although I don't remember the game myself, my grandfather swears that Buffon vs. Milan (think it was '95 or '96) was the best goalkeeping he'd ever seen.
Pirlo vs. England was an amazing performance, despite the game being relatively boring. Considering Pirlo was done, after the full season he had with Juve and the way he almost single handedly spanked England was, not simply something you admire, something you'd show any midfielder learning how to play the game.
Ariel Ortega vs. Jamaica in the '98 World Cup. Granted not the biggest of occasions, but he was unstoppable. Scoring two, supplying another two and being instrumental in every play they had. They had 3 players on him and he just trolled them by passing the ball, evading the defenders like an offshore account does tax fraud, before picking the ball up again and strolling away with it. His finish for the first was sensational, brilliant technique, his 2nd was brilliant and his passing was as great as you'd want from any Argentina #10 and I still can't believe Argentina only scored 5 that day.
