I put about $10,000 worth of stereo into my Magnum (got a smokin' deal at $7,000 if you can believe that!)...
Kenwood DNX9140 is the best head unit I was able to find as of last September in terms of features. The only thing it lacks is internal storage (hard drive), which for me isn't a big deal b/c it has a USB port and an iPod connector so between the two of those devices, I can't see a need to store anything on the head unit. Sirius, back-up cam, the whole 9.
Whole car is Dynamatted, IMHO you shouldn't waste money without taking this step first.
Focal amplifiers, Focal 3-way components for a front stage, Focal composites for the rear stage.
Image Dynamics sub, 12", dual 4-ohm voice coils.
Lotsa fiberglass and wood, Stinger wires, misc. adapter modules, LED lighting, etc.
The sound is absolutely crystal clear up to the point that you just can't stand the volume any more. But there's a downside - all your sources will start to sound like junk. Sirius used to sound as good as a CD on the stock system, but now that you can hear the difference, Sirius sounds like dookie compared to a high quality MP3 or a CD. So be warned, you may not like it as much as you want to.