The Display

(The image isn't actually this fuzzy, it's just my camera.)

The display I used is a VFD (Vacuum Fluorescent Display) from I got one with a 2x20 display and 7 buttons. It was designed to fit in a 5.25" PC bay, so it fits perfectly in the CD compartment in my dash.
It has a serial port interface, which makes it very simple to program, just initialize it and send some strings across.
I chose the VFD over the cheaper LCDs, because the LCDs are only rated to 122°F, and I live in Phoenix, where my car hits 140°F in the summer.

The commands

 Scroll up through track list*. Scrolls a menu up in menu mode*.
 Scroll down through track list*. Scrolls a menu down in menu mode*.
 Restarts the current song. Scrolls to the previous menu in menu mode*.
 Next track. Scrolls to the next menu in menu mode*.
 Enters menu mode*. Selects the current menu option*.
 Restarts the daemon and client.
 Toggles random play.

* Not yet implemented.