my all time favorite head units are a few Kenwood models that have a "self-hiding" feature. When you turn off the car, the face flips over completely and looks like you bought the car without the stereo option. (blank, panel cover)
by the way, if you know where i can get one... let me know.
i would say the high end denon units, clarion drz9255, mcintosh, prs880, all nakamichis, alpine 7998, 9815, 9887, eclipse 7100, theres a lot of fine units out there, but exponentially more poor quality ones
i like the denon, and mcintosh units the best, i used to own a mcintosh, but sold it to buy a new car. lol paid for the whole thing, now i got a clarion drz9255 that isnt as good as the mc, but its still better than almost everything else.