Bob Beamon's record of 29' 2 1/2" was the first to come to mind for me too. Beamon's record, was broken by Mike Powell on 8-30-91 with a leap of 29' 4 1/2", but is still an Olympic record that stands after 32 years!
I had a college instructor, who was also the track coach, who sincerely believed Beamon's record would not be broken for 50 years, that it was that much of a milestone.