Enter your games in to GAMEYE. If their value seems worth your time, then double check the current market value by checking recently sold listings on eBay or by using Price Charting.

If the value is still there, I would say eBay is your best bet unless you happen to know of a community of gamers where someone may be looking for the title (like, say, a retro gaming convention) If you try to take it to a retro game store, they'll (necessarily) low ball you since they need to make a profit.