All Along The Watchtower gets my vote as well, simply epic and utter perfection. I don't believe in gods, but if anything would convince me otherwise, it's Hendrix.
Tuesdays Gone - Lynyrd Skynyrd. I personally think it's a better song than Free bird, it's actually one of my favourite songs ever and top on my iTunes most played by over 100 plays, my ultimate chill out/relax/calm down song. This live version with the strings intro makes it even more amazing.
Third? What else but Baba O'Riley by The Who. Nothing more needs to be said, just listen to the sound orgasm that this intro and song itself is.