Local mom 'n' pop specialty shops are going to be the best, if you happen to have one nearby. Usually you get a fair deal near market price, without the bloat from eBay and Paypal taking cuts.

Thrift stores and yard sales have occasional great deals, but for the most part everyone knows if their item is worth something these days, so almost only junk goes there. And even if the donators don't realize, I think most thrift stores will filter valuable items out and sell them online.