I am not the best person to discuss the North Jersey/NYC dealers, so I will leave it to people such as the wonderful Rcprince...
I can speak at length on what is in and around the Philadelphia area. There are several dealers, but I believe that things are better in NJ/NYC. Although, you will not have to put up with as much attitude here, in most cases.
Here is a short list of a few of the high end dealers in my area:
1) Community Audio. Chestnut Hill(NW) section of Philadelphia. John Adams is the owner, and a very, very nice guy. I consider him a friend. The greatest asset is that he will allow you to listen in a relaxed, no pressure atmosphere, yet will be as involved in guiding you along as you would like. Brands: NAD, Jolida, Cambridge, Rega, Rogue, Linn, Naim, Electrocompaniet, Totem, JMlabs, Nova, Osborn, Music Hall, Creek, Ixos, RedGum, etc.
2) Stereo Trading Outlet. Jenkintown(5 minutes north of Philly), PA. Mike Leshner is also a very good guy(also a friend), and his store has always specialized in used, high end equipment. He also carries new products, but I feel the discounts offered for the used merchandise overshadowed the new stuff. You can also listen in a relaxed, no hassle environment. A visit is only necessary if you are interested in listening to the used inventory, as an up to date list is on their website(www.tsto.com). Brands: any and all used, Paradigm, Pass Labs, Canton, Marantz, Sherwood Newcastle, Sunfire, Cary(limited selection, but I guess he can order it), PS Audio, etc.
3) David Lewis Audio. Northeast Philadelphia. Ah, now we get into a guy who a lot of people absolutely abhor as the typical, nose in the air high end dealer. Dave Serota is the owner, and I find him to be better in person than over the phone. I deal with him well, and even purchased my Jadis amp from him. Yes, he is opinionated. Yes, he might tell you that you will not be able to listen to anything else today. But, I believe he honestly tries to offer his customers the BEST in audio. And, will not carry a brand he does not believe in. In terms of sound, support(why he doesn't carry Jadis any longer), and the whole package. Store really does well in terms of tubes(especially SET) and vinyl. No HT. Brands: Air Tight, Cary, Kimber/Kimber Select, Synergistic Research, Nordost, VAC, Vans Evers, Montana, Monitor, NAD, JMlabs, Acoustic Energy, YBA, Audio Refinement, etc.
4) Soundex. Willow Grove(5 minutes north of Jenkintown), PA. OK, here is another place that could be considered a bit snobby. But, I find them to allow one to listen in whatever manner they like. Yes, they are there to make money. And, yes, they think they are audio dieties, but they carry very high level equipment, and will allow you to do pretty much what you please while you are there. They are pleasant in person. The place is massive, and you could easily get lost, or spend an entire day there. Along with the industry, they went HT in a very big way. Brands(reads like an 80s - 90s Murderer's Row): Audio Research, Mark Levinson, Krell, Martin Logan, MIT, Wadia, Dynaudio, Proac, etc.
HiFi House. Jenkintown and Broomall(20 minutes west of Philadelphia), PA. Relaxed and good people. Sort of the normal high end retailer. Brands: B&W, Definitive Technology, Bryston, Paradigm, etc.
I would like to mention some others. Danby Radio, who carried B&W, Alliante, Sunfire, and Conrad Johnson, but I believe they may have closed, so I cannot fully list them as a place to see. David Mann Audio is also OK, but I wouldn't really take time to see the store. Quest For Sound is also in Northeast Philadelphia, but isn't a store, but an e-tailer(sells out of his home) here on Audiogon. Good brands, but you will be doing business over the net, and will not be really going there in person.