If you're not headed out to a farmer's market this weekend, another great option for Tokyo-ites is C-Cafe in Mitaka. The third Sunday of each month they host an outstanding organic buffet (tabe-hodai or all-you-you-can-eat) for a mere 1,000 yen. Featuring vegetables from a local organic farm, it's hard to beat for flavor, health, and fun. And while it is a bit out of the way, Keta-san's curry is enough reward for the effort you'll expend.
Check out my article over at Eco+Waza describing it, and then mark your calendar for the September buffet! You'll be glad you did.