You need to list your games. If you want the most cash Amazon, Ebay and Craigslist might be a better option. If you want to just trade it in quick Bestbuy, Gamestop, Walmart, Target, local stores and Amazon might take it for more depending.
I'm not sure but I've seen a few posts where CAG'S have said Wal Mart has some good trade in values. You might want to check with them but don't hold me to that as I've not done any TI's with them personally.
The poster above me though is quite right that the HDD size will play an important factor.
Sorry I couldn't be of more help but good luck buddy.