Overview

Resveratrol is a naturally occuring compound found in foods including red wine, grape seed, and peanuts. Alone, it has anti-thrombotic activity. It is also present in red wine, where it is responsible for some of the cardiovascular effects of that beverage (along with the alcohol, catechins and proanthocyandins? in wine). (abstract (cache))

For those who choose not to consume alcoholic beverages, there is an an herb that is rich in resveratrol. The root of Polygonum cuspidatum is actually the richest known source of resveratrol, and it has long been consumed in Japan, where it is known as Itadori tea.

Purified resveratrol supplements are relatively expensive; this one runs 36 cents per day. It is not clear if the hypothetical benefits justify the expense, although some people take resveratrol for other reasons.

References

PDR Health, the website of the Physician's Desk Reference, has an overview of resveratrol here (cache).

Int J Tissue React. 1995;17(1):1-3.
Antiplatelet activity of synthetic and natural resveratrol in red wine.
Bertelli AA, Giovannini L, Giannessi D, Migliori M, Bernini W, Fregoni M, Bertelli A.
Institute of Anatomy, University of Milan, Italy.