Prior to traveling to California, my wife and I kept hearing good things about In-N-Out Burger, a California based fast-food chain.
After having two meals there (once outside Sacramento, once in Burbank), we both agree that the good reviews are justified. The hamburgers are excellent – juicy and fresh-tasting with crispy lettuce and fresh tomatoes and onion. The vanilla milkshakes are quite thick and the french fries are good but slightly different than the crispy fries one typically finds at fast-food places.
Several downsides: a limited menu (no chicken, fish, special burgers), a longer wait for your food as it is prepared fresh, and the restaurants are only limited to four Western states.
Overall: very good and fresh fast-food.