A slightly sideways rec: Beth Gibbons* & Rustin Man – Out of Season. Not altogether folky, but then my description of folk wouldn't include Band of Horses, and they are a magnificent band.
Has no-one mentioned Iron & Wine? Start at their album The Creek Drank the Cradle.
More americana: Giant Sand (and also Howe Gelb in his own right). These might lead you onto non-folky bands like Smog/Bill Calahan and the Silver Jews.
*Yes, her out of Portishead