I've had excelent luck with KEH.com over the years. I've done OK on E-bay as well, but I actually prefer KEH.com.
I've bought two different Nikon Bodies. An N-80 in EX condition for my sister to replace a stolen N-50, and I also picked up an N-70 for myself back in January. I've bought several different lenses for both Nikon and Canon cameras, and also a Nikon SB-28 flash. All of these with the exception of the N-80 were in bargain condition, and all have worked as they should. The N-70 shows the most use, and is a little rough looking. But it works as it should. Additionally, I paid very little for the N-70 camera, so I'm not complaining. Several of my lenses that I bought from KEH are in better condition then the E-bay listed lenses that were in EX condition.
KEH is my first choice for used gear.