In my humble opinion, when it comes to an extended intro, nothing can possibly beat "Shine on You Crazy Diamond," with "Riders on the Storm" close second.
As far as kick-ass intros, it'd be hard to beat Metallica "Master of Puppets," Alice in Chains "Would," and Slayer "Seasons in the Abyss." I've always loved Iron Maiden "Wasted Years" with a sick riff as well. Reading most of the choices listed, perhaps I have different notion of what a "best beginning" is.
As far as kick-ass intros, it'd be hard to beat Metallica "Master of Puppets," Alice in Chains "Would," and Slayer "Seasons in the Abyss." I've always loved Iron Maiden "Wasted Years" with a sick riff as well. Reading most of the choices listed, perhaps I have different notion of what a "best beginning" is.