One of the foods highest in omega-3 fatty acids, salmon is a great choice on top of a bit of hand-pressed rice (nigiri sushi), in a roll (maki sushi), or many other ways.
Another good source of omega-3s, tuna is a popular choice for sushi, inside a roll or served on top. You have to be careful with tuna -- bigeye, for example, can be high in mercury
Many popular sushi rolls incorporate avocado, often with fish and vegetables but sometimes alone with the rice (and nori, sushi’s seaweed wrapper). Avocado is high in heart-healthy fats and fiber, and it's packed with other nutrients.
Sushi doesn’t have to include fish. For the seafood-shy or vegetarians, veggie rolls (with things like avocado, cucumber, carrot, mushroom, onion, asparagus, and tofu)
A classic in sushi, the California roll includes rice, nori, avocado, cucumber, and “crab” (usually surimi, or imitation crab, made of pollock, egg whites, sugar, and other stuff).
This is the Mount Everest of sushi, a combination that can include crab (usually imitation), salmon, shrimp, at least one kind of tuna and sometimes other fish.