Parts list so far:
Basically a motherboard with a ARM processor that can run Android 4.0 right out of the box.
Case to hold a Mini-ITX motherboard (I assume the PandaBoard will fit) and can be put into the double-DIN slot of a car stereo head unit.
This is listed to fit on the case listed above. However, it’s only single-touch. Might have to look for other options in the same size.
This is listed on the PandaBoard wiki as a good, fast card for the purpose. I plan on having music on this, but not movies, so 8GB should be enough.
12V -> 5V DC-DC Converter
Car batteries put out about 12V, while the PandaBoard runs on 5V. Having 4 amps is recommended, especially with a few USB accessories (which we will have, in the form of GPS and AM/FM radio). The linked model can handle 10 amps, so there’s plenty of overhead.
OBD-II -> Bluetooth Adaptor
I bought one of these already. It lets your Android device connect to the on-board computer for logging speed, RPM, oil temperature, etc., as well as viewing and clearing engine codes. Using the Torque app handles the device side. While Torque’s wiki page warns against the cheap adapters on Amazon/eBay, this one worked just fine for me on both my Android phone (LG Optimus S) and tablet (Asus Transformer).
Total so far: $485
I may have to blow the $500 limit to get a multitouch screen. I also haven’t included the GPS and radio modules.
For parts specific to the RX-8, I need:
Double-DIN Stereo Face
Nothing too interesting. It just replaces one bit of plastic with another bit of plastic that will fit better for my purposes
Also pretty boring. This connects the manufacturer’s stereo plug to the aftermarket unit. You’ll need to dig a little to find one to fit your car.
Edit: It turned out that the stereo face came with its own wiring harness. This may or may not be true for your car, so try to check before ordering.