Ive used keh, ebay, and bhphoto. depends what Im trying to get and where I can find it, for example I got a 400mm old nikon film lens for cheap on bhphoto. but when I was selling my old canon gear the auction was pretty low on ebay so I imagine that would be a great way to get started with full frame digital. I wish I would have kept the camera and had it converted to infrared if I had known it was going to sell for so low, a bit after I sold it my old nikon I got off a friend and had converted to infrared died