A must-have installation.  Fairly easy to install.  Make sure you install with the parking brake!  Failure to do so most commonly results in not being able to take out the key from the ignition!

You can install all over the place (DIN unit; custom mounting between the DIN unit; on top of the dashboard, glovebox).  I preferred mine kinda hidden, non-intrusive, but easily accessible. 

Overall shot:

Closeup of unit: