Car audio specialty shop/Crutchfield.
I really wanted an Excelon deck, but to get the dual zone audio I would have to get a deck that was ugly and wouldn't work well in my car (face always flipped up, and as it is the deck is very high in my dash), so I got a Kenwood 6025. It also does two aux in, which is another requirement. It replaced an Eclipse deck that didn't have aux in. Its main function was that it played MP3s, but it didn't have direct access to tracks, which was a downfall.
I like lots of features, have specific needs, and it needs to sound okay at reasonable volume. Doesn't need to wake up the neighborhood, don't need to hear it outside the car with the windows rolled up. Need to be able to listen to different source in front and in back without external amps, need remote, WMA and MP3 playback, direct track access, and most of all, CHEAP.