(http://infohost.nmt.edu/~armiller/japanese/tea.htm)

Introduction
Green tea is the only kind of tea grown in Japan. It is drunk hot or cold, and is always served straight without milk or sugar. It is primarily produced in Shizuoka Prefecture which is about 150 km southwest of Tokyo. Harvesting of tea leaves begins in May; young tea leaves are valued. Japanese teas are primarily steamed and non-fermented, rather than roasted and semi-fermented (as with many Chinese teas).

Ryokucha    緑茶
This is a generic term for Japanese steamed teas, using the Chinese characters for "green" and "tea".

Sencha  & nbsp;煎茶
80% of all green tea consumed by Japanese is sencha tea. It is a high grade of tea that is made by steaming the leaves to stop fermentation and changes in color. The steaming helps to also reduce the bitter flavor of the tea. The leaves are then crushed and dried, and packaged for sale.

Gyokuro    玉 露 
A top grade of tea, made in the same way as sencha, but with tips of tea leaves that are sheltered by bamboo screens as it matures. Kabusecha is similar to gyokuro but it has been covered for a shorter period of time.

Maccha   抹 茶 
This is used in tea ceremony and in cooking. It is a high grade tea and is grown screened as is gyokuro tea. After the leaves are steamed, the veins of the leaves are removed and the dried leaves (tencha) are ground on a stone into a powder. Maccha is not steeped; the powder remains in the drink. Hot water is poured into a special bowl and the tea is whisked with a bamboo brush. The tea is bright green and sometimes foamy, with a strong taste. This powdered tea is often used to flavor foods such as ice cream and cakes. This way of drinking tea was first recorded about 1200.

Bancha    番 茶 
This is a lower grade tea, and is less expensive, because it is made leaves that are older and less tender than those made into sencha. These tea leaves are picked in the summer and autumn rather than the spring.

Kocha   紅 茶 
This is what the Japanese call most black teas, served primarily European style with milk and sugar or with lemon (often called "miruku tei" or a "remon tei").

Hojicha   ほ うじ茶 
This is a roasted tea which combines sencha and bancha leaves. The roasting process turns this leaves brown and the tea has a strong flavor and fragrance. It is thought to be good for the digestion.

Genmaicha 
Also a roasted tea, genmaicha is made of bancha and sencha leaves combined with roasted rice. This tea also has a distinctive fragrance and considered to be healthful.

Kugicha 
This tea is made with the leaves and twigs of the tea bush. It is thought to have less caffeine than the other steamed teas.

Other teas drunk in Japan and elsewhere:

Oolong cha   ウー ロン茶 
Oolong is a semi-fermented tea (compared to the steamed green teas and fermented black teas). These tea leaves are primarily grown in Taiwan and the Chinese provinces of Fuchien and Chianghsi.

Jasmine cha    ジャ スミン茶 
This is a green tea that is flavored with the blossoms of the jasmine plant. It has a pleasant aroma. It is best served at a medium strength; any stronger and the tea may become astringent.

Pu-erh cha
This is a cheap and cheerful Chinese tea. A small amount can steep large quantities of tea, so often this is served in restaurants. It is dark brown and slightly astringent.

Genpicha
This is a slimming tea which is popular with women. The idea is that the tea produces a slightly diuretic effect. The author has not tested its effects but I hear from my brother-in-law that it's pretty awful and can only be drunk hot to tolerate it.

Mugicha   麦 茶 
This beverage is not made from tea leaves but is brewed from barley kernels. Japanese people commonly drink it cold during their long, hot, muggy summer season. It has no caffeine and no calories. This tea is sometimes served hot as well in Korea.

Konbucha   昆 布茶 
Again, this is a beverage made not from tea leaves but from soaking konbu (seaweed kelp) in hot water. Often konbucha is brewed and reconstituted into a powder which can be mixed with hot water. Sometimes it is flavored with shiso leaves. It has a rather salty taste and is considered to be healthful.

References: 

Japan, an Illustrated Encyclopedia [Kodansha International, 1993]; Shizuoka Prefecture 
Japanese Proverbs and Sayings [Buchanan, University of Oklahoma Press, 1965]