Any real "diner"
Growing-up fave: Mastori's in Bordentown, NJ (outside Trenton) is a "diner" that "just growed" and wound up huge. It's the only place I find myself wishing I were a snake with a jaw I could un-hinge to be able to take a proper bite of a burger.
Last-few-years fave: Ken's House of Pancakes in Hilo, HI. Imagine a diner with asia-pacific fusion cuisine and locally-raised free-range beef...
Recently-discovered: Castaway in Burbank, CA. Looks like it's gonna cost an arm and a leg. It doesn't. A friend took me there in October... wow. Nice view, too!