I've been to a number of Korean markets in the NYC area, but Hanyang Mart on Northern Blvd (near 150th St) in Flushing/Auburndale might be the best one I've found in the NYC area. There's a lot of energy on a Saturday afternoon at Hanyang, with a bustling parking lot, outdoor food stands and lots of sampling stations. I was fascinated by the rice cracker machine spitting out discs of crackers at 2 per minute in small explosions of roasted rice.
In the parking lot near the entrance was a mountain of nappa cabbage that was probably slightly past its prime that was on a mega sale, and being picked through by a small horde of people. Also as you enter the market, there were several hundred cases of korean pears that seemed to just hit the market. Each pear probably weighed a pound, and they were perfectly crunchy-sweet. Case of 8 (or 10?) went for around $23. Also in the entryway of the market is a snack shop with a lot of fried things, packaged items and behind the counter were large vats of hot liquid for boiling noodles and such. The menu on the wall was all in Hangul, so I couldn't figure out what all those goodies were with a quick look-around.
The produce aisle was packed with many of the goods that you find at places like Hon Au Reum in Koreatown or Woodside, but in greater quantity, and from the looks, quality as well. There was a small stand near the back of the produce section where two women were pickling vegetables in a hot red paste, and packing other cooked items. The seafood section was also stocked with some unusual items. I was only there to look around, but I couldn't resist the monkfish liver (ankimo) for a very reasonable $5.99/lb., as well as a pack of baby octopus for something like $3/lb. There was a separate kimchee and prepared foods section with what looked like great deals on non-commercial hand-packed stuff.
Perhaps the only section I didn't quite notice being so top notch was the meat section, but I may have just overlooked it having been overwhelmed by everything else.
The only problem is that this place isn't accessible by subway. It's a long walk or a short bus ride from the Main St station. Otherwise, it looks like a short walk from the Murray Hill LIRR station. But it's certainly worth checking out if you're in the area, or if you have a vehicle.
150-51 Northern Blvd.
Flushing, NY 11354