https://www.youtube.com/watch?v=dZJPYo-YUkA It was always going to be a toss-up between this and the previous entry, but when you really boil it down, Slayer's inclusion on this list wouldn't even exist without Sabbath - and that's discounting the fact that on a purely sonic level Iron Man is just so monolithically unmovable as a metal riff, it deserves to top any future list too. From the bed of distortion that seeps out across the speakers thanks to Tony Iommi's godlike (and plastic) fingertips, he bends an open string from behind the top of the guitar neck to create that sense of distant power chords approaching only to fade away. Then, after a few of these measures have played out, the very definition of what somewhere in the world a teenager is describing as 'DAT RIFF' comes thundering in, bringing with it a completely ageless composition, and a performance that ensured Sabbath would always be remembered as the shining example of pure metal. It's not just the perfectly doomy guitar tone that makes each chord rattle into the next, it's the triple-slide that heralds the riff's high point on the neck, before plummeting all and sundry back into the depths of hell along with the band and ushering in a lifetime of imitation that to this day is still annoying guitar-shop workers nationwide. Are there any omissions you would have rather seen on the list? (Most definitely!) Let us know in the comments which riffs are your favourites!