If you are looking for conveyor belt sushi, visit Nemuro Hanamaru near Tokyo station and Midori in Yurakucho.
If you are looking for more high quality, Hashida in Kachidoki has the best sea urchin sushi. Lunch course costs only 3,500 yen and I felt really reasonable for the quality.
This photo is a plate from Hashida, when I had the lunch course.
The area where famous sushi restaurant is of course Tsukuji. You'll be able to find delicious sushi for sure.
Other than that, I've been to Miyako in Shinjuku Hyatt. You will taste unforgettable sushi!