Gazelle.com buys and sells used electronics over the web. During the iPhone 3GS launch week, their front page offered money for old iPhones, and they managed to score a mention in a NYTimes blog post, which is how I found out about them. I gave 'em a shot with my old iPhone and am pleased to say it was a good experience.

Details for the wary: You register, then describe to them your item for sale, its condition, what parts it still has. From that, they give you an "offer." When I did it a couple of weeks ago, for an iPhone 3G with all cables in "good" condition, they offered $210. If you accept the money in the form of an Amazon.com gift certificate, you get a percentage bonus, in my case another $10. For some items, especially iPhones, they send you a free shipping box in the mail. You pack your item in the box with some crumpled newspaper, apply the postage-paid label, and drop it in the mail.

You get confirmation emails throughout the rest of the process, including one saying they received the item, and one saying they inspected the item. The inspection is the scary part, of course: if they disagree with your description, they might make a new lower offer. According to their standards, my iPhone was not "good," it was "fair," and they explained they didn't like the scuffing on the back of the case. The new offer was $40 less. I could reject the offer and they would send back the item, but of course I just took the money.

Overall, it was a good experience, and much more convenient than eBay or hawking it at work. I can't think of a way the inspection process, a natural weakness of this kind of interaction, could have been improved. The solid design of the website and the free shipping box go a long way to build trust prior to the transaction, and that's much appreciated.