I was listening to Zep's Dazed and Confused today and the rocking middle section of that song never ceases to amaze me - John Bonham was from a different planet, was completely insane, or both. Nothing I've ever heard in any other song quite compares to that.
Honorable mentions:
Neil Peart on the songs Tom Sawyer and Subdivisions
Tommy Lee on the forgotten Crue song Red Hot, and just about everything else he did on the Shout at the Devil album was superb
Dave Grohl was great in Nirvana, and is probably as much a reason for their success as Cobain was