B&H photo is reputable
Some folks like Cameta Camera
Stay far away from eBay and any deal that is too good to be true.
I would not hesitate to take their prices and walk into a loal Ritz or other camera store and negotiate a price. I
Where did you end up buying it...?
I have a D3100, and I would buy it again. Easy to use... fast shutter speed, HD video.
If you buy from Cameta, see what is available in additional lenses. I nabbed a zoom and wide angle for only a few hundred. They have great packages on their ebay store.