As you would expect, there are plenty of fish restaurants in Tsukiji, both inside the wholesale market and also in the narrow streets that surround it. The rows of simple, hole-in-the-wall eateries in the very heart of the market cater primarily to the early-rising market workers who are already finishing their lunch by the time the rest of Tokyo is still digesting breakfast. But most are happy to cater to casual visitors, providing you know what you want and don't hang around too long.
How to find the best places? Just look for the lines outside.
Daiwa-zushi is small, cramped and simple in the extreme, but the quality of the fish is superb, the prices are good and the service is never anything but friendly. Cognoscenti of prime seafood make regular pilgrimages here from all over town. It's become so popular it's had to expand next door (it now holds 20 people instead of 10).