What is some of the most recognizable intros in rock and pop?

I want to know what songs you can think of that almost anybody would know within a few seconds of the song playing.

Here are a few I thought of off the top of my head:
http://www.youtube.com/watch?v=P-AYAv0IoWI
http://www.youtube.com/watch?v=CGhMp6yECpU
http://www.youtube.com/watch?v=87yq372R4Ts

**Youtube links are more than welcome, have fun!

Deep Purple - Smoke on the Water
Jimi Hendrix - Purple Haze
Iron Butterfly - In-A-Gadda-Da-Vida