I'll guess the Zep and 'Finger.
Gaz
Got the obvious one (Stairway...).
Peter Finch type hint: The other was my favorite when I was, uh, 18.
I just realized something tonight while listening to the replay: I never got the opportunity to enjoy "Stairway" on its own merits because it had become a cliche by the time I encountered it. What a drag.
P.S. It is perhaps even worse to know what you want at 18. Discuss.