I have found success in selling original nintendo and super nintendo games on Ebay. I can usually find them for decent prices at garage sales, goodwill, and flea markets.
When i first started checking out shopgoodwill, i was able to get some decent buys, but not lately. They have jacked up their shipping and handling fees, which pretty much negates any profit that was available.
I still check it on a daily basis, just no luck lately.