Podpacker is a service that buys your CDs then downloads all of them on a new iPod.
You send them an e-mail telling them what music you want to sell, they send a guy over to take a look at your CDs. In a few weeks you get a new iPod sent to you loaded with your music. You don't get your CDs back, but you do get a free iPod equal to the value of the CDs you traded. The minimum (100 CDs) gets you a Shuffle. The max (450) gets you an 80 GB system. It's a great thing if you have a big collection of old CDs that you love.