Not all fish sauces are created equal...not by a long shot. Most of the crap you get in a supermarket comes from Thailand or Singapore and is made with water, sugar, MSG and anchovy extract. Pure garbage.
Enter Cuong Phan. He was a refugee from Saigon that settled in California in 1979. He really missed the flavor of the fish sauce made by his family in Vietnam. So he bought a small factory on Phu Quoc Island and started making his own fish sauce, Red Boat. It's made like wine. He draws the liquid from salted anchovies and ferments it in wood barrels for over a year.
There are only two ingredients in this stunning fish sauce: anchovies and sea salt. The sauce has a very rich and smooth complexity. It tastes unlike any fish sauce you have ever tasted. You really need to have this in your pantry. Let me re-phrase that: you absolutely must have this in your pantry. You can buy it here: http://redboatfishsauce.com/