I sure can't remember them all, but I was at the very first U.S. show by Led Zeppelin, in Denver on 12/26/68 (I was 14), when they opened (without advance billing) for Spirit and Vanilla Fudge. They were awesome, and we eagerly awaited the release of their first album some weeks later. I just watched the Led Zep dvd on my system, and I recommend it to anyone who was ever a fan.
A few others that come quickly to mind:
Frank Zappa (couple times, including performing Joe's Garage in Berkeley - fantastic show)
Jimi Hendrix (Denver Pop Festival, 1969, last performance of Jimi Hendrix Experience)
Big Brother & Janis Joplin
Moody Blues
Jethro Tull
Johnny Winter
Iron Butterfly
Creedence Clearwater Revival
Joe Cocker
Three Dog Night
Zephyr
The Flock
Persuasions (acapella in a small club - terrific)
Big Head Todd & Monsters
Bela Fleck
Modern Jazz Quartet
Ahmad Jamal
Miles Davis
REM
Lots of others that I don't recall at the moment
