It is the second to last day of Gibson's countdown of the Top 50 Greatest Guitar riffs of all time. Today they roll out No. 11 to 20. Here are just three: 15. "Enter Sandman," Metallica (1991): Metallica's oh-so-sinister riff in "Enter Sandman," the first single from their self-titled fifth album, is one of their heaviest and most ominous, which is saying a lot from a band who defined heavy and ominous. But what really makes "Enter Sandman" a master-riff is just how catchy it is, which explains how it quickly became one of, if the the, signature song from the kings of thrash metal. The bottom-heavy and propulsive riff grabs you buy the throat at the very beginning and never releases. Sleep with one eye open, indeed. – Sean Patrick Dooley
14. "Purple Haze," The Jimi Hendrix Experience (1967): This wonderful, woozy rock and roll song purportedly originated when Jimi Hendrix's manager, Chas Chandler, overheard him playing the riff backstage in 1966 and persuaded him to flesh it out with lyrics. "Purple Haze" appeared the following year on Are You Experienced. "I dream a lot and I put a lot of my dreams down as songs," Hendrix told New Musical Express in 1969. "[Purple Haze] … was all about a dream I had that I was walking under the sea." – Ellen Barnes
11. "Crazy Train," Ozzy Osbourne (1980): The late Randy Rhoads' signature riff propelling "Crazy Train" down the tracks was pure metal genius on many levels. Released as a single simultaneously with "Mr. Crowley" – both from Ozzy's debut solo album Blizzard of Ozz – "Crazy Train's" riff is wonderfully melodic, and it perfectly conveys dark, almost schizophrenic, imagery through the frenetic rising and lowering of alternating notes. The riff's structure makes you feel, well, crazy – sort of like you just might be going off the rails. Easily one of the greatest riffs of all time, and the one most copied by aspiring metalheads. – Sean Patrick Dooley Check out today's full list here