do a search of the audio forum for "dynavin" you'll find 3 or 4 active threads on this unit. It is a china-made aftermarket headunit that looks completely OEM and is probably exactly what you are looking for. It is completely plug and play, has a ton of versatilty in the form of RCA in's as well as iPod and USB hook up for all your own music. It is retailing for $649 from one of the sponsors and looks really, really good. I have one on order, as it's like a 3 week + wait for shipping.
The only real draw-backs that I have seen are no satellite radio support and you'll need the AC relocation kit which I think I paid $40 bucks from Tischer BMW.