Los Angeles area
Pink's (W. Hollywood) -- chili dogs
Langer's (MacArthur Park) -- best pastrami sandwich on the planet. Yes, better than anywhere in Chi or NY. Best meat. Best bread. Ordinary mustard.
Philippe's (Downtown. Prounounced Felipes for some reason) -- Home of the Original French Dip (and it is) -- for lamb dip. Tourist Beware. Philippe's mustard is seriously hot. No matter how hot you think it is, until you've tried it, it's hotter than you think. YOU HAVE BEEN WARNED. Once you've tried it, "It's Hot, But Good."
Saigon Bakery (Alhambra) -- banh mi, especially their homemade head-cheese.
Gene's (Monrovia) -- Homemade sausage grinders, Friday only. Homemade milanesa grinders, Thursdays. Pastrami dip as good as The Hat's. A local gem. Everything else's good, too. Great fries.
The Hat (SGV) -- Pastrami dip. Okay, you have to understand that a pastrami dip is nothing like a pastrami sandwich. The quality of the pastrami is completely different. For whatever reason pastrami dips are a big thing in SoCal, especially in the SGV.
Apple Pan (WLA) -- hamburgers. Don't ask me why. There's nothing you can point at to say why they're the best other than that everything works in perfect harmony.
King Tacos (ELA) -- Tortas of various sorts. My favorites are lengua (tongue), asada (grilled beef), al pastor (marinated pork), and mollejas. A torta is a sandwich made with taco meat on a Mexican roll (bolillo). Of all the wonderful taco places in LA, I chose the King chain almost at random. They're very good, but there are others just as good.
It's a big town. I'm sure I forgot a few of my own favorites, and there are plenty I don't know about or underrated.