I always give away my old games. Why only gt a 1/4 of what I paid for them to sell them for several times what they paid me? It's an insult.
My brother traded in games one. 20 games for $50. He was desperate and needed the money, but I was not happy.
Anyways, most of my games come form Steam for $10 (got to love that summer sale).
Also, craigslist and ebay are wonderful for used games if you really want to sell them.