Never been to an OG or WC, and never been outside North America, but attended MANY meets from 1962 through 2002, so here's some memorable marks/races I witnessed in person (not on TV).
BOTH HSR's in the mile by Jim Ryun (3:55.3 in 1965) and Alan Webb (3:53.43 in 2001).
A "WR" in the 6 mile by Billy Mills and Gerry Lindgren in 1965 (27:11.6).
Leslie Maxie's still-standing HSR in the 400H (55.20) in 1984.
Ron Clarke's 2-day double of a 5K in 13:25 and a 10K in 28:13 (1966??).
Vicki Huber's CR of 8:47.35 in the 3000.
Gerry Lindgren's 1964 10K victory against the Russians just after graduating high school!!
Peter Snell's 3:54.9 mile when he destroyed the field with a 24.5 final 220 yards!!!
Gerry Lindgren's indoor HSR of 8:46, when he challenged the great Gaston Roelants, who won in 8:41.
Some of the more memorable ATHLETES I've seen (but can't remember specific times/marks I saw them make) are:
Maria Mutola, Lance Deal, Al Feuerbach, Bob Hayes, Henry Carr, Henry Marsh, Annette Peters, Bob Seagren, the great El G, Murray Halberg, Bob Schul, Dyrol Burleson, Ulis Williams, and too many others to list!!