The Ronnie Lane ARMS Benefit show in 1983 was pretty cool, featuring Eric Clapton, Jeff Beck, and Jimmy Page, playing together along with a ton of other rockers:
The 2-day Tibet Freedom Concert had an all-star line-up too - The Smashing Pumpkins, Beastie Boys, A Tribe Called Quest, Pavement, Cibo Matto, Biz Markie, Richie Havens, John Lee Hooker, Red Hot Chili Peppers, Rage Against the Machine, Sonic Youth, Beck, Foo Fighters, Björk, De La Soul, Fugees, Buddy Guy, The Skatalites, Yoko Ono/Ima and No Doubt.
Went to some of the Lollapalloza shows, and if anybody ever heard of the Day on the Green shows in the Bay Area, well, I went to a bunch of those all day/night shows with 5+ bands at each show (YouTube search "Day on the Green" and you'll see what I mean)...
ADG