If you like Stairway To Heaven, listen to this song from 1968 by a band called Spirit. Considering that Stairway wasn't recorded till 1971, I guess it's obvious where Jimmy got one of the guitar parts from:
http://www.youtube.com/watch?v=ogTFdlbup24
Apparently Spirit toured with Led Zeppelin early on in 1969. There's also a story that Jimmy Page got the idea of using a theremin from seeing Spirit's guitar player use on on stage.