Has the KK Cafe really never been mentioned here?
Was surprised that a search turned up no results. Yes, it's an awful name, and easy to pass by (It's on 252 Divisadero at Haight, right near King Foot Subs); with an extremely uninviting store front.
However, they have one of the best burgers I've had. I've always felt the key to a good burger is what you mix in with the meat; and it tastes like they mix in cumin (it's owned by a Chinese couple, which would make sense given the use of cumin in authentic Chinese dishes) with the meat, among other things, and it's just a delicious, old-fashioned burger. You can get a cheeseburger and fries for $5.95, too. The fries are good, although perhaps frozen. The meat is likely not organic, or houseground, but it certainly is delicious.
Super-friendly owners, and they also sell peanut milk here, which is one of their own creations and definitely a unique experience.