The outdoor Brooklyn Flea Market is one of my favorite places in all of NYC, and also my #1 take-guests-to destination. It is the most perfect place to start your weekend. You don't necessarily have to do any shopping– it's the view of downtown Manhattan from the market that really does it for me. And of which I realize I do not actually have any photos... I'll fix that once I am back in Manhattan.
The merchandise, too, is fantastic in my opinion. Everything is one of a kind and reasonably priced for vintage & antique items. It mainly contains clothing, jewelry, furniture, and interesting knick-knacks from all over. Once there, you can see that the vendors have worked hard to complete their collections of never before seen items. In other words, it's an established and mature market. It really is a sight to see; all the merch is simply intriguing.
The trip is usually completed by the perfect early summer morning weather, breezes from the water, and the walk from the subway to the market. Street vendors are smart enough now that they know all the shoppers will be passing through the Bedford Ave. subway station (the dreaded L train), so you will also be presented with an assortment of another twenty or so thrift shops and vendors along your walk. Oh and awesome street art is always a plus.