Metallica and NIN had too many awesome rock intros/lead ups to count but in my mind the this is the opening that will never be topped.
http://youtu.be/y1s5gbJEEbg
You know, I had plenty of ideas for this, but, yeah, THAT one pretty much is the ONE. That song is one of the greatest songs in rock and roll history. Every time it comes on while I'm driving I crank it up until my ears ring.