Jason/mods, please don't move this to the Audio section. Being most people don't view that forum, I thought this would help the good amount of people that are getting the iPod adapter.
I started another topic a while back asking about what a good choice for a USB flash would be. After a ton of research, I settled on the Corsair Flash Voyager 8GB. I've had the unit for about three weeks now and can give a brief synopsis of its overall quality.
It's encased in sturdy and firm rubber padding. Tests have shown that you can run it over and it'll remain in pristine quality. This is unlike many earlier USB flash drives that were in normal plastic housings that could break without much harassment.
The unit I bought in particular is the 8GB version, which holds roughly 1,300 songs in 320kbps quality. A main factor in considering a flash drive is it's read speed, and the Flash Voyager is the fastest unit on the market (outside of its more expensive brother the Flash Voyager GT). It's average read speed is 38 mb/s, which is a great deal faster than other drives that average around 8 mb/s. Even if you're sending FLAC quality songs through your amp, there won't be any lag time in requesting the song and it appearing through the speakers.
The MAJOR plus in running a USB flash drive instead of your iPhone/iPod as the host of your MP3s is that iPhones/iPods process the audio signal and they do it in analog only. Flash drives on the other hand don't do any of the processing at all. They hand that task over to the unit installed in your car which in turn does it digitally, thus giving a more pristine representation of the original MP3/WAV's quality.
The Voyager comes with a USB extension cable that allows you to clear the height restriction in our tiny armrests. Overall I think this is the ideal piece of hardware to use with the iPod adapter that many of us will be getting. If anyone's interested, Newegg has a good deal on it: