I've got a Kenwood KDC-W6527 head unit in my car, and at the moment I am more than happy with the sound, it should have been around 300 quid, and I know its a lot for a unit that will primarily be using the aux in, but its features are wicked. I've put a review in the car audio section of this site, so take a bit of time to read it if you want to there are loads of places you could buy one online, letsbuycaraudio dot com or justkenwood couk
Its loaded with functions, and when I wanna remove the PC, it can play cds with mp3s on them. Its a shame all my archived ones at 128kbp sound like cack.
At the moment, its ipod-tastic as I have not got enough parts yet to build my baby!