Smashburger.
I don't know what they have in there, but it's awesome. I go there every Friday.
Also, outside of their super sauce, I dig Super Duper Burgers as well. Any burger place that offers "secret sauce" I pass, but I can tolerate Super Duper.
Non chain ones, I like this place called Big Mouth Burger in San Fran. That thing is so straight up, no shenanigans kind of a burger, just the way it should be.