The best INTRO track...

My current favorite is Black Sabbath - Wheels of Confusion / The Straightener. The first 8 seconds are godlike.
 
I like the fire of Satanic Warmaster 'Raging Winter', the warlike sirens of JC, the electro beats of Secrets of the Moon 'Inverted Kaos Principles', the spoken opus of Deicide 'In Torment In Hell, and the whole 'I.T.D.S.' of Nile yes!

edit: etc ...
 
Um, do you mean intro track as in ANY first track on an album?? That's a bit...open... or any track intended as an intro, and not a 'proper' song? That seems a much more appropriate question, in which case, Emperor's Alsvartr no competition. Otherwise, I haven't got a friggin' clue.