As noted by TUAW, online retailer Amazon has updated their electronics trade-in program to include Apple devices like older iPod touch and iPhone 3GS models, iPod Classics and original iPads. The webpage is available here, Amazon states it’s currently in “beta” status and items have to match several criteria to be eligible for the program. The devices have to be working units of course, must be in good hardware conditions, and mailing one back to Amazon (though a separate retailer handles the program, Amazon still provides the backend interface) will get you credits to spend on Amazon.com.
Prices seem to be pretty convenient, too: trading in a third-generation 64 GB iPod touch will result in $156 of credit, whilst an old 8 GB iPhone 3GS is priced at $162. A WiFi iPad 1st gen with 16 GB of storage has a trade-in value of $235, and a 16 GB iPad 2 (WiFi) is listed at $330.