Hank Williams III
Hellbound Glory
.357 String Band
Joel Kaiser & the Devil's Own
The Devil Makes Three
Old Crow Medicine Show
Wayne Hancock
Check out Those Poor Bastards as well, top notch stuff (Rachel Brooke did a duet album with Lonesome Wyatt, but down at the Barnyard is her best album)
Not sure if they're country, but they're in the ballpark, and that is Deer Tick... favorite band right now (excluding their most recent album).
Also, honorable mentions should go to Graham Lindsey, James Hunnicutt, Highlonsome, Slackeye Slim, Willy Tea Taylor and Nick 13.
Nice, not everyday I see a Willy Tea reference.
I'd add Matt Woods and Whitey Morgan.
Overall, have to go with George Strait. Just had his 59th #1 at country radio which I believe breaks the record for most #1's in any genre in history.
Among new acts, my vote right now goes to The Band Perry. "If I Die Young" was a huge hit for them and it was recently certified Quadruple Platinum for 4,000,000 total downloads.