A couple weeks ago I found this ice blue with red splatters painting at the flea market. It's an unmounted canvas so the vendor gave me a smokin' good deal. I picked up a black canvas to staple it to, and I'll probably frame it using my old trick.
If you're ever in NYC over a weekend, you should stop by the Antiques Garage (or this place!) in Chelsea. It's literally a parking garage that they lease out to flea market vendors on weekends. Two giant floors of awesome finds. If you see me there on Saturdays, I'd be happy to point you to the best vendors. But go early! They are usually set up by 9:30 or 10:00 am and the good stuff is pretty much gone by noon.
I would say about twice a month one or two of the vendors has brought in an artist's collection. It usually means the artist has passed away and the family is selling off their estate. So while you won't get any of the artist's masterpieces probably, you can usually buy a great piece from a moderately sucessful NYC artist for a great price.
Much of the art in my home, including both of the pieces above and below, were sold at the flea from an artist's estate sale. The pastel was $5 and the giant, framed watercolor was less than $100.