We have a local and grass-fed meats butcher in Rhinebeck (and Kingston) NY called Fleisher's. They have two ground meat products that have, at least for me, revolutionized burger-making.
One is ground 'bork,' which I'm sure you can figure out. Amusingly, one of the staff there is trying to convince customers that it's a kind of hybrid. The burgers I made from it the other night were amazing.
Only to be superceded by the burgers made from the beef/bacon mix. Oh my lord, the burgers from that were enough to make me forget my name for a good half hour.
I have a new, semi-frou-frou burger trick that I've developed. I always pack the burgers as gently as possible, and so season them on the outside with salt and pepper. I have taken to putting chopped shallots on the seasoning plate, too, and lightly pressing them into the surface of the burger. The shallots get caramelized, and even a little burnt--which tastes great!