Russ Hodges calling Bobby Thomson's HR has always been my favorite. The circumstances surrounding how it got recorded are pretty amazing, it's been discussed on here before but it's a great story.
(taken from Wikipedia) Ironically, if not for the generosity of a Dodger fan, this famous moment in sports broadcasting might have been lost. This was in an era before all game broadcasts were recorded. However, in his autobiography, Hodges related how a Brooklyn fan, excited over what appeared to be a certain Dodger victory, hooked up his home tape recorder to his radio. The fan wanted to capture Hodges "crying." Instead, he recorded history; the next day, he called Hodges and said, "You have to have this tape."