In-N-Out Burger is way more prolific through California but in the LA area , you just can't beat Tommy's Chili Burgers. I have to make a disclaimer that there is a Tommy's 1 block from my old high school, so I may be a little biased.
Beware of imitators , there are many places that go by variations, such as; Tommi's , Tomas', etc...

http://www.originaltommys.com/

I hope they come up to the SF Bayarea, but it does give me someplace to go whenever I'm in LA.