Fastest guitar solo I've ever heard was Angel of Death by Slayer.
Greatest ever... wow, I don't even know if I could narrow it down. How about Slash's lead in Paradise City and Sweet Child of Mine. SRV was already mentioned for Texas Flood. I'm a big fan of the live version of Tight Rope. EVH and Randy Rhodes for Eruption and Suicide Solution. Dimebag and George Lynch should be thrown into the group. I don't think Jake "the snake" Sabo of Skid Row was ever given enough credit for his solos. Hmm... I need to think about this some more.
Speaking of which, what ever happen to guitar heroes?