I would avoid the NY places like the plague--gray market stuff, missing accessories, bait and switch, etc.
The ONLY places I would do business with are KEH (out of Atlanta) and B&H out of New York. You may find cheaper prices for new stuff, but you will get a much worse deal in the end if you go somewhere else. KEH has excellent prices for used stuff and represents it fairly.
Digital Cameras are a bit different than traditional film cameras.
As people have covered before, the focal length of the lens (50mm) indicates the magnification of the lens. For Digitals, 1x magnification is about 35mm, so a 300mm lens is about 9x magnification and a 15mm lens is 1/2 x magnification. Too Much magnification can be bad, as you get camera shake (rule of thumb is to use no SLOWER than 1 over the focal length of the lens (so a 300mm lens needsshutter speed of 1/250 or 1/500 or 1/1000, etc. If you use 1/125 or 1/60 or less, you will start to get blurring from camera shake).
The other thing that is important is the aperture of the lens--the 'f' number. This is how much light will get into the lens. It is expressed as f stops, but they are basically a fraction. If you have a lens that has f 2.8, then it transmits (very basic explaination) 1 over 2.8 of the light that comes in the front of the lens (or about 1/3 of the light makes it through the lens to the film). An f4 lets 1/4 of the light to the film, an f1.2 lets almost all the light to the film. The downside to low F numbers is cost. An f1.8 lens might be $100, but an f1.2 in the same focal length might run $600 (they need a bigger body, better coatings on the lenses, etc to get all that light through with no loss).
Exposure is based on a combination of shutter speed and aperture--a 'correct' exposure for your camera in a given situation might be 1/500 shutter speed at f8 aperture. You can vary this combination by say closing the aperture to f16 and changing the shutter to 1/250, or opening the aperture to f4 and increasing the shutter speed to 1/1000. This gives some creative control (the first modification gives more depth of field to the picture--more is in focus, and the second modification would freeze the action better).
So, you need to figure out what focal lengths (as in a Zoom Camera) you need for your photography, and the lowest f # you can comfortably afford.
That being said, if you are new to the field, I would go with something like this:
Tamron 28-300mm lensUse it for a while, and once you start getting comfortable and realize--"hey, all my pictures are in the 100-200mm (or 28-75mm, or 200-300mm, etc.) range, you can start to look for a lens more suited to your photography. This lens has a different f stop rating for each focal length--at 28mm focal length, it has an f3.5 rating, but at 300mm it has an f6.3 rating (more light is 'lost' at the longer focal lengths due to the design of the lens.
AFARR