Since sushi is a "dish" rather than a single ingredient, it is important to consider all of the parts when talking about nutrition. Nori (the seaweed wrapper) is very high in iodine, while ginger and wasabi contain various antioxidant compounds, as well as vitamins and minerals.
Perhaps the most sought after benefit of sushi for most people is the easy and tasty access to concentrated forms of omega-3 fatty acids. This "good" form of cholesterol helps to balance out and even eliminate "bad" cholesterol in the body, helping to prevent clogged arteries and a bevy of related health concerns, including atherosclerosis, heart attacks, and strokes.