Chatuchak (or JatujakThaiจตุจักรweekend market in Bangkok is the largest market in Thailand. Frequently called J.J., it covers over 35 acres (1.13 km²) and contains upwards of 5,000 stalls. It is estimated that the market receives between 200,000 visitors each day. Most stalls only open on Saturdays and Sundays.
The market offers a wide variety of products including household items, clothing, Thai handicrafts, religious artifacts, collectibles, foods, and live animals. (from Wikipedia)

The Chatuchak Weekend Market is HUGE! You can easily get lost here, so if you are in a Group, make sure to set some place as a meeting point. They have everything here. This is also a good source for those hard to find plant seeds.