Just to make things a tad more complicated on the aftermarket HU front:
I've gone with a Sony XAV-701HD in mine. Can usually find it on sale for about 100$ off MSRP somewhere. I went with this because I really liked the multimedia features of the unit itself. It was faster than the Pioneer, straight-forward to use (unlike the Kenwood), and up until recently, had a TomTom nav module you could use with it. The module could be removed for updates/etc through the same TomTom software that is used for their PNDs. TomTom has delivered some software patches/updates to the system as well. The 701 was a popular model at the shop I had the work done for the install, with employees picking it for themselves (3 of the 6 on staff at the time either had a 701 prepping for install, or had one on order).
In general, compared to the previous models, the current 601BT/701HD models are a huge improvement in performance and responsiveness, and can have nav added to the system. There is a catch though, that prevents me from really recommending this for someone who wants built-in nav...
It took me nearly a month just to find one of these modules, and Sony isn't saying why the US model is gone, while they are still selling a similar model in the EU. So, if you do want the module, it's going to be a bit of a slog before you get one. Those that get the modules seem to keep them.