The Brooklyn Flea is another treasure trove of odd finds, cool artifacts, and handmade goodness. If you're looking for inspiration or just something cool to hang on your wall, you can probably find something here. And if all that treasure hunting leaves you hungry, you are in luck--there's a delicious assortment of local food vendors and artisans there too.
As Jim Jarmusch put it in the documentary Blank City, the address is roughly between Bowery, Avenue B, 14th Street and Houston. This area of the city is steeped in art, film, and music history; so many hugely influential artists, film makers, and musicians still live and work here. For such a small area, I think it's had more concentrated influence on contemporary art and culture than anywhere else.
The best underground shows you will find will have free pbr and models as far as the eye can see. They are rarely announced, so keep your eyes out for promising openings, especially with Milk Underground coming up.
This place has one of the hottest rooms I've ever been in. The combination of barely being able to breathe from the heat to immediately jumping into a freezing murky pool is addictive. There's also a great roof patio for a change of scenery. A good old school New York spot.