Fox Sports has a list of the Top 10 perfect performances in sports history.
Because You Tube is awesome, you can see that uneven parallel bars performance, here, along with other Nadia clips:
Christian Laettner gets a shout-out for the 1992 NCAA East Regional Final game against Kentucky-- one I've replayed in my head and on my VCR countless times with delight since that year.
Again, because You Tube is awesome, you can see that buzzer-beater, here.
And, the incomparable Secretariat, of course.