Via Sean I see this list of great moments in pop music history. The list doesn't appear to be definitive, just a collection of important moments. Sean has some comments, and solicits discussion, so if you have anything to say, go drop him a comment or two. (He's trying to jump-start his blog after going away for two weeks, I think.)
I don't really have much to say, since I don't really know that much about the history of pop music, but there are a couple of omissions I'd include:
:: "The Day the Music Died" -- Buddy Holly, Richie Valens, and the Big Bopper die in a plane crash.
:: Pink Floyd's Dark Side of the Moon's release date, whenever that was. Didn't that album stay on the charts for something like 800 weeks?
:: Jerry Garcia dies (1994 or 1995).