Many good ones here so far. I'll add add a couple:

Ohio - CSNY
Eminence Front - The Who/Townsend
Last Train to Clarksville - The Monkees
Pipeline - D. Dale?
Balck Magic Woman - Santana (not sure if that's the intro, or the main riff)
Passage to Bangkok - Rush
Do It Again - Steely Dan
L.A. Woman - The Doors