Services like Gazelle and ecoNew are great, because you can sell them your old, unwanted gadgets for a decent price, and they'll be recycled, which is better than just throwing them in the trash. Ecosquid makes this process easy.
Instead of manually entering in your info on multiple sites, Ecosquid acts like an Expedia or a Priceline or an Orbitz, searching all those sites for you and spitting out the best offers. An example!
Above is the 16GB iPhone 3GS. The top four offers are there, giving you a pretty comparable payout for sending in the phone. There are some more results below too, like AT&T, Motorola, Best Buy, reconnect, Apple and Cell Phones for Soldiers, plus two more pages of various organizations that offer $0 for your stuff. My guess is you won't make it past page one most of the time.
Ecosquid! Just like you're not going to search individual airline sites unless you're married to one specific carrier for luxury or points reasons, you probably don't care which recycling service your old junk goes to. [Ecosquid]