Mamob's Cafe - Glendale. Fantastic Cuban fast food.
Watson's Drug Store and Soda Fountain - Orange. Classic American diner food in classic American diner setting. 100+ year old location.
The Filling Station - Orange. An actual converted filling station. Awesome atmosphere, great for patio eating.
Rutabegorz - multiple locations (Fullerton, Tustin, Ornage). Specializing in vegetarian/vegan cuisine, though they've got non-veggie options as well.