Things that come to my mind immediately. sorry if its biased towards India
Sachin's 143 against Australia at Sharjah (What a knock! took us to the finals)
Saeed Anwar's 194 vs India (I was biting my teeth in anger, but it went on and on)
Dhoni's 183* against Sri Lanka (it was a day when he was in his zone totally)
Sachin's 98 vs Pakistan in 2003 WC (Its a classic, especially that 18 run over of Shoaib who spoke so much before the game)
Kaif's 87 vs England - Natwest 2002 (Both Kaif and Yuvraj were inseperable that day, with Kaif bringing on his best act of his life)
Most are that of India's. The thing is, I watch 99% India matches, and very rarely do I appreciate the opposition's knocks (One rare one was Anwar's which I appreciate now)