While it wasn't the best farmer's market I've ever been to, it was hands down one of the best in the Washington, D.C. area. (It might tie with Eastern Market).
There were at least two dozen different food vendors and then a handful of artisans displaying beautiful clothes, jewelry and paintings.
I bought a hearty mixed olive bread from a vendor who drove all the way down from Baltimore to display her fresh baked breads. It was only $6, not too bad. I bought corn on the cob -- $0.50 per ear and a scrumptious homemade gouda cheese for $6.
There were several vendors selling herbs, plants and flowers, which was a nice touch. All in all it is an affordable farmer's market filled with a variety of fresh produce, vegetables, meats.
If you're in the area on a Saturday make sure to check it out! It's definitely worthwhile and you'll likely strike up a conversation with any of the friendly vendors.