2001 Mercedes-Benz S-Class S500 4dr Sedan (5.0L 8cyl 5A)
This has been a love-hate relationship. The dealership has been great about fixing things, but now that I'm out of warranty with 57k miles, it seems like too much is going wrong. Tire pressure sensors, AC failures, oil leaks... despite all that, it's the most comfortable ride I've ever owned. Great balance between smooth handling/feel and keeping in touch with the road.
Umpteen-way power seat and nav system.
Phone interface/phone are ancient and not upgradable. MP3/Ipod interface. Update NAV system look and feel.