Greatest Rock Riff EVER! Poll

Do you like your music heavy? I like all kinds of music but as a guitarist I don't think you can beat a good riff can you? Ones that stand the hairs up on your neck and just roll off the fretboard!

I'd like to start a poll which I'll add to as people put forward their favorite. I'm going to set the ball rolling with possibly my top 2, but I'm sure someone will change my mind. Here we go:

Painkiller - Judas Priest: http://www.youtube.com/watch?v=JAagedeKdcQ
Riff Raff - ACDC: http://www.youtube.com/watch?v=5uXu067MTqI