For those into photography, there are several vibrant communities out there that offer a place to discuss, argue and show images ... whatever floats your boat. I tend to frequent DPReview.com for that stuff.
But when it comes to buying and selling equipment, there are only a few places I would trust for that. Nikonians is a pretty good marketplace I have heard, but they started charging just to see posts and that turned me off completely.
Fred Miranda does not charge for buying of equipment, and I did some of that over the last year or two. But they do charge for selling equipment ... 24 bucks per year. Pretty cheap if it works.
And I have to say that it works very well ... they have a nice system allowing you to show images for free (you need to host them somewhere and you can pay a bit more to have them hosted on site.) They have an excellent feedback system that shows you every comment made about every person on there. It is so effective in self-policing that I have no qualms about trusting people who frequent that site.
I actually made my first "for sale" post about three weeks ago. In it, I listed my Canon G10, my old Nikon 70-210 F4 (which had gone unused for 2 years), an L-bracket for the D2Hs, which I sold 18 months ago, an expodisc (white balance tool) and light meter than I had not used much at all. It took less than a week to sell everything and I ended up selling it all for about $720cad. That's not bad at all for stuff I was no longer using.
So I did it again this past week ... and so far my PayPal balance is above 2200usd (which includes deductions for me buying a new Japanese rice maker by Zojirushi on eBay and a used Wacom Intuos 3 tablet on fredmiranda) ... this is enough to pick up a used D700, which I am targeting soon. Although Nikon is so anal about supporting US cameras in Canada that I may just buy from an eBay seller in Canada and eat the extra 300 bucks to get a warranty.
This is a very effective way to recycle your old stuff ... anything that you thought you needed but really didn't. Anything that was relegated to the benches by a new and better piece of equipment. And fredmiranda.com is a great place to shop ...