Just had a great one at Bull and Beggar in Asheville, NC. 4 bucks with purchase of a (alcoholic or non-) bev on Mondays, comes with fries. Everything we had there was great too.

If you're ever in an unfortunate enough situation to wind up in Macon, GA, the Rookery has great burgers.

My favorite burger remains the burger at Holeman and Finch, though.

In fairness, I don't eat tons of burgers, and these are just what I thought of off the top of my head.