How much is my camera worth?

Okay so i've had my Nikon D3100 for about 2 1/2 years. There's absolutely nothing wrong with it, except the lens is a little scratched (but you can't tell when you take photos) and there a few scratches on the body of the camera, and also, it makes a little noise when it focuses.
I don't know where to go to figure out what it's worth because I would like to sell it and get a different camera. So is there anywhere I could take it? Or do any of you guys have a guess at would it could be worth?

Amazon sells some used equipment as does Adorama. Check their prices for a judge on what yours will fetch. Also, factor in the scratches and drop the price say $50 because of them.

One very important thing. Somehow get the shutter count on this camera. The shutter count on any dslr is as important as the millage on a used car. As yourself, would you buy a used car if you didn't know the millage? Of course you wouldn't. Same here.

Look around from software that will give you that information. Software is out there for my Canon cameras so I know it's got to be there for yours.

I want to know how much my Nikon F8700 with filters and scope worth today