The Tokyo Metropolitan Central Wholesale Market (東京都中央卸売市場, Tōkyō-to Chūō Oroshiuri Shijō), commonly known as the Tsukiji Market (築地市場, Tsukiji shijō), is the biggest wholesale fish and seafood market in the world and also one of the largest wholesale food markets of any kind. The market is located in Tsukiji in central Tokyo, and is a major attraction for foreign visitors.
Tsukiji Market consists of an inner market where most of the wholesale business and the famous tuna auctions are taking place, and an outer market whose retail shops and restaurants carter to the public.
The "outer market" (jogai shijo) is a mixture of wholesale and retail shops that sell Japanese kitchen tools, restaurant supplies, groceries, and seafood, and many restaurants, especially sushi restaurants.
The outer marker opens regularly on weekdays and Saturday, but is usually closed on Sunday and public holidays. But to make sure they are open, check the calender (2010/2011) on website. (the red dot indicates the market is closed)
Also, be careful that most of the shops in the outer market close by the early afternoon.
There are some sushi restaurants in the outer market, which often serve raw fish in "don" style. (don=丼; Rice bowl topped with sliced raw fish)
Kaisen Don ( 海鮮丼）－Rice bowl topped with a variety of sliced raw fish
Uni-don(ウニ丼）－Rice bowl topped with Sea Urchins
There are also conveyor belt sushi restaurants.
Be sure you visit the market on Saturday when all the gloceries and restaurants are open.
The link below provides further information about Tsukiji market.