What's the best way to find used photography equipment?

I know there are a bunch of photographers on here so I was hoping you guys could steer me in the right direction. Yesterday, I bought a used Canon 20D body and am now in the market for a 18–55mm lens, but they’re few and far between on Craig’s List and overpriced on eBay. Are there websites that cater specifically to used photography equipment? If so, are some more trustworthy than others?

Thanks!