B&H and Adorama are reliable, I have bought from both with no problems. There are many other online sellers, but a lot a not kosher.
I just had a problem with "The Camera Professionals" and want to warn all of you. When I ordered, it showed the camera is in stock, I got an confirmation e-mail and even had to call them to confirm my credit card and again was told the camera is in stock, picked and will ship the same day. Well, two days later I get a camera, but its not the one I bought and paid for - it was a model about half the price of the ordered one and it was a re-conditioned one, too. So I called immediately and was told the camera is out of stock and i should keep what I got!! Hell no!! Finally after speaking with some kind of imbecile (who was telling me that I have to pay myself for shipping it back etc), I got the super on the phone. She told the camera is out of stock and supposed to be back in a few weeks, but she agreed that it was their mistake and she would send me a shipping label to ship it back. Well, this came a week later and I shipped the camera back asap. They have it now back, but my money was not credited, yet - may take 3-5 business days. I surely will check every day my credit card. While this all really pissed me off, I called again and had friends calling for the camera I wanted, and we were told, that it is in stock, weird. There are many reviews for these dealers, but a lot are fake. I did some research and came up with the following web site:
http://www.sheddingsomelight.com/buy-cameras/list/dealers-allstarfam.html
Whenever one will buy something over the net, please check here, it may help you avoid some trouble.
Also, make sure that the camera comes with everything that is listed at the camera makers info.
Some years back, when I decided to buy a Canon Digital Rebel, I found a source on the net that nearly sold the camera a third cheaper than any store. I finally decided to order via internet, and was asked to call in to confirm your credit card number (this always should raise your attention). When I did so, I was told that I only ordered the camera and lens for this price. The battery and the charger were extra and together (with the shipping cost) it was just a tad under a local store that eventually got my business (as another store got it yesterday for the camera I wanted from the Camera Pros - a bit more, but I brought it home right away and it has everything, its new and has proper warranty)