Zen and Leaves: Japanese Tea Ceremony is a brief introduction to the history and significance of the tea ceremony.

Chaji is a detailed description of the tea ceremony where a meal is served.

The Japanese Tea Ceremony entry at Wikipedia is quite extensive. There is a brief description of a tea ceremony followed by more detailed information about: history, equipment, types of tea ceremonies, the tea ceremony meal, and studying for the tea ceremony. There are sections that explain the influence of the tea ceremony on: calligraphy, flower arranging, kimono, and tatami. It ends with references, further readings and external links.

Essencha is a local (Cincinnati, Ohio) "contemporary tea cafe and tea store whose goal is to provide the very best the tea world has to offer." They sell many varieties of tea, from black to green to herbal. The site gives basic information about each tea.