Sushi is commonly eaten with condiments. Sushi may be dipped in shoyu, soy sauce, and may be flavored with wasabi, a piquant paste made from the grated root of the Wasabia japonica plant.
True wasabi has anti-microbial properties and may reduce the risk of food poisoning. The traditional grating tool for wasabi is a sharkskin grater or samegawa oroshi. An imitation wasabi (seiyo-wasabi), made from horseradish, mustard powder and green dye is common. It is found at lower-end kaiten zushi restaurants, in bento box sushi and at most restaurants outside of Japan. If manufactured in Japan, it may be labelled "Japanese Horseradish".
Gari, sweet, pickled ginger is eaten with sushi to both cleanse the palate and aid in digestion. In Japan, green tea (ocha) is invariably served together with sushi. Better sushi restaurants often use a distinctive premium tea known as mecha. In sushi vocabulary, green tea is known as agari.
Source: http://en.wikipedia.org/wiki/Sushi; Sept 28, 2010