The Kenwood Music Keg KHD-C710 is similar to a trunk CD-changer—but instead of six CDs, you use a 10GB hard drive cartridge that can hold about 150 CDs' worth of MP3 or WMA files ripped at 128 Kbps. You transfer them from your PC using a USB 1.1 docking cradle and software developed by PhatNoise.

You have to use the Music Keg with a Kenwood CD-controlling radio that was built after 1998. We paired it with the Kenwood KDC-MPV622 ($280 street), a CD/MP3/WMA-playing, Sirius-capable in-dash receiver with excellent sound, small buttons, and 67 garish display settings. For music lovers with lots of digital audio files, the Music Keg is more convenient than the rip-as-you-go in-dash units from Pioneer and Sony.