The Shot Heard Round The World
Avi posted about the Zidane headbutt, and we've been (and probably will continue) discussing it there. In the meantime, for anyone who hasn't seen the play, here it is.
For those interested, here's a longer version of the play, where you can see everything develop before and after the play.
After watching that clip, am I the only one who wishes that he had headbutted Buffon too? That would have made him my favorite player of all time.