Craigslist, eBay, KEH (I generally go in that order). Usually you'll get a few bucks less on Craigslist than eBay, but selling local usually works pretty well and pretty quickly for me. And no eBay \ PayPal fees. eBay tends to drive the price a little higher, but then you have to deal with shipping, which for some items can be a pain. KEH is usually my last resort for selling as they are usually 50% of what I can get out of gear elsewhere (same with
Best Buy).
We just got a pair of new phones from Best Buy, they offered $35 for my better half's BlackBerry Tour (mint condition) and $80 for my HTC EVO, also mint condition. I will get near $200 out of my EVO on eBay (due to the included accessories) and ~$90 out of her Blackberry.
Right now on my local Craigslist there is a body only D60 listed for $320, a D60 w/ kit for $325 and a D60 w/ 55-200 and Nikon bag listed for $525. That last one is probably a bit high, but then again EVERYONE on Craigslist will try to haggle you down. I don't think I have ever had a single person want to pay my asking price, which is always a very fair price. Consider pricing it a little higher so that when you haggle down, you actually get what you want for it.
The D7K has proven to be pretty reliable thus far. Unless you have a genuine need for a second body or a son or daughter that has a budding interest in photography that can use it right now, sell it. DSLR bodies, especially entry level models, depreciate in value quite rapidly.