Alpine and Nakamichi are IMO the best looking decks in a Bimmer. The Nakamichi looks oem even, but does not give you Mp3 playback. They do feature AUX-ins though, so you could link your iPod.
As a cheaper alternative to Alpine or Nak, the Kenwood KDC-MPV5025 has selectable illumination that can be changed to match the BMW illumination almost perfectly. It also has Mp3 playback...