IMO, stay away from sony. They're not complete shit, but you can have better.
Now keep in mind, your mp3 player uses a USB cable to connect to the computer, but in most cases it wont' play through the USB. HU's with USB connections are usefull for hooking up to external harddrives. What type of mp3 player do you have, as that's critical in determining whether or not a USB connection would even work.
Either way, I'd find a headunit with AUX input, most new ones have them now. I'm a big pioneer fan, they've got great stuff. Panasonic HU's are pretty decent too, as of course are alpine units.