I have the Pioneer AVIC-D3 with everything you can add for this unit. (around $640 online)
Bluetooth and Mic for cell phone
XM- Satellite Radio w/ Real time XM-NAV traffic
Rearview camera
iPod control adapter
USB connector (for thumb drives and hard drives)
Female RCA plugs for game console and power converter.
It's true that you can only have one DVD in at a time, but it's a minor inconvenience that I never really experience, since all my music and videos I can run it off my iPod or hard drive. As far as quality of the unit, it sounds better than the old Alpine I used to have in my Z.
And yes Kenwood is a nice unit, but it also costs double. If you need to have top of the line everything, Pioneer is not for you. But if practicality, value, and quality is what you're looking for it's a known fact that AVIC-D3 is the best bang for your buck.