IIRS, most of the car hard drives are 40-60GB rugged drives that are not worth the price. Last one I saw for sale was a 40GB for 150. I would just get a 32GB or 16GB flash drive which can be had for much cheaper. Hell, for my stereo, I usually have a 1GB el-cheapo flash drive I got from shuttle (came with a thermos as well. Totally worth the free I got it for!) for music, and occasionally a 4GB plugged in whenever I watch a video on it (I occasionally have to wait in the car for a hour or so when I get stuck taking my brother to soccer practice, I watch divx videos off my stereo).
Oh, and as an FYI, JVC receivers are limited to 250 folders with 999 files in each folder for a usb drive.
And as for stereo's with usb ports, my JVC has a 6 foot usb cable coming out the back that I have routed to drop below my glove box. It is awesome, and I don't have a usb drive sticking out the front of my stereo.