With the E36, the head unit was a standard DIN unit, and it looked it. A new one could be dropped in pretty easily, and if the right unit was used (Blaupunkt Sydney), would look like it belonged with the car.
BMW has gone with the 'designed into the dashboard' look for the E46. I hear it is really a standard DIN unit, but it doesn't look like it. I was wondering if anyone has done an aftermarket install, and what it ended up looking like. If anyone has any pictures, please post them or a site with them.