Chia seeds are produced by the salvia hispanica plant, a member of the mint family, which is native to Mexico. It was grown by the Aztecs as one of their major food sources. It is an annual that grows to 3 feet tall and produces purple or white flowers.
According to Dr. Andrew Weil's website, salvia hispanica seeds are rich in omega-3 fatty acids, and are a good source of fiber and other nutrients such as calcium and phosphorous. They can be eaten raw or ground into a powder and eaten as a cereal.
Monterey Bay sells chia seeds by the quarter-pound or pound. Puritan's Pride offers 16-ounce containers of the seeds, with frequent two-for-one specials. GNC carries chia seeds in 12-ounce bags, while the seeds are available from True Foods Market in 1-pound, 5-pound, and 55-pound sizes.