Good list.
I've heard of quite a few. Let me make some recommendations:
The Carolina Chocolate Drops are awesome. Traditional old time southern field and slave songs. And some new stuff, too.
John Mellencamp. You know him.
Darrell Scott - Dude is an IBMA Hall of Famer. Even if you've never heard of him, I'll guarantee you've heard his songs. He writes for a ton of people. He's also a Wintergrass regular.
Peter Rowan - See Darell Scott, only he's been around longer. Also a Wintergrass regular.
Justin Townes Earl - One of my personal favorites. Steve Earl's son. A better songwriter, too, if you can believe it. His firs record, "Yuma," is one of my all time faves.
Elvis Costello - You probably know him from his 80's electronic years. The guy is a seriously talented artist, and has been on an acoustic bender the last few years.
Johnny Cash you know. His son just released an album of unreleased songs. And while I'm all in favor of more J.C., I can understand why some of these songs didn't make it to release.
Avett Brothers - Fantastic duo from the Carolinas.
Bob Dylan you know.
Black Prairie. Three fifths of The Decemberists. Not nearly as morose, though still kind of mellow and blue. Good band out of Portland. Their fiddle player is a fantastic person.
This list is missing two artists, though
Jason Isbell's latest release "Southeastern" is nothing short of a masterpiece. I know it probably isn't "acoustic enough" but that is some awe inspiring songwriting. If "Elephant" doesn't make you choke up and cry, you have no soul.
The Milk Carton Kids should be on everyone's radar. They're channeling Simon and Garfunkle up there.