Mumford & Sons
Believe it or not, folk musician Laura Marling can be credited with this Grammy-winning group's assembly. Many of the Mumford band members played as Marling's backing band, until they formed their own unit in 2007. But as Marcus would later tell Entertainment Weekly, it was this early experience with Marling that not only hooked him up with his folksy posse, but also taught him a thing or two about hitting the right notes: "Laura would show me the two buttons that I press on the accordion, then I make a noise and it’s in the right key. Sometimes I would even put stickers on the buttons so I knew what to press."