Not sure if this is the best site, but try www.gazelle.com I was offered $234 for my iPhone 4S, didn't take it, but was curious to see what I could get out of it.
Just checked my old phone (droid x) on Gazelle and it was worth $20. However, I sold it on ebay for $75.
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Never try and teach a pig to sing. It frustrates you and irritates the pig.