This page was written in 2004, so it goes without saying that it's extremely out of date...
To download MP3s to my Archos Jukebox Studio 10 [100K PDF; local copy], right now I have to plug it in to my PC via a USB cable, and either manually copy the files across or run a script that will do that. I can't leave it connected all the time (like iPod owners seem to do) or it will run its batteries flat. Also, I often leave it in my car's glove box and forget to bring it in at night time.
I'm after a better solution to this. Something wireless would be fun.
Right now if you want to play MP3s in your car, you have a few choices:
Use a portable hard disk player like an Archos or iPod
Use a portable CD-R player
Use a portable flash-card player
Use a removable car hard disk player like empeg
Use a car CD player that can play MP3s off CD-Rs
The idea here is to have a hard disk player that is fixed in the car but can be accessed over the air, perhaps with Bluetooth or 802.11. The player would listen for incoming connections, and allow access to the media library. With any luck the power consumption in idle would be low enough that it would not drain the car battery too much to leave it on even when the ignition is off.
When you have a file you want to add to your car player, you simply drop the file into a directory on your desktop somewhere. This would wake up the player in the car, copy it over the air, and shut the player down.
If you want to implement something like this with a PC inside the car (which is much harder on the battery to run 24/7), you could do it a different way: instead of waking up the player remotely and accessing it that way, make it synchronise with the PC whenever you start the car up.
A more achievable goal would be to produce something with a USB host controller and a WiFi interface that will let me download MP3s to the device over the air from a queue directory on my Linux box.
One thought is to build it as a CPU plus USB host controller, and use a USB WiFi interface to handle the networking. The Philips ISP1362 (official page, datasheet) can drive two devices, so it would be perfect for this.
This might make a fun university engineering project.
NetGear MP101 (ARM9 based, 802.11e), NZ$340 (US$200?)
cd3o network mp3 players, US$150 (or US$200 with S/PDIF output)
Sound Blaster Wireless Music, US$200
Squeezebox, US$280
Some USB 1.1 devices, controllers, etc.
Igor Cesko has managed to get an AVR to speak USB without any external components -- bit-bashed USB! He has published source code (for non-commercial use only).