A good source for good looking buttons is to find some kind of OEM pieces for your car that someone is selling broken.. IE Broken OEM radio, etc. You can chop them up and make the button panels part of your dash. If you don't like what the buttons say, a little acetone will take care of it for you.
For those of you to which this might not be immediately obvious: to wire up the buttons, just chop the cicut board up until you are left with the contacts. Use a voltmeter to find which two contacts close with the button push and solder onto those.
For interfacing to OEM Knobs.. There are two types of knobs you will generally find in cars also.. Potentiometers turn smoothly, and ALWAYS stop at a minimum/maximum level. They are generally hard to interface directly to a computer without some sort of other electronics that can read the pot and return a value (skill: moderate). The other knob is a switching knob.. These click into notches when they turn kind of like your mousewheel and they spin around indefinately without stopping. These knobs are really easy to hook up because each click is a momentary button press. Just find the contact that momentarily closes when you turn the knob clockwise and the one that closes when you turn counterclockwise (they may have a common ground) and hook it up!
You can also often hook into the backlight systems and make your buttons light up with a little LED. Usually, to save money, all the buttons are lit with one LED or other lamp through a plastic diffuser located above the circut board. You just put your lamp on the end of this so it shines into the diffusor and viola! I found a place behhind my dash that was on the stock stereo harness that gives voltage based on the console dimmer, so I can build a small circut to brighten/dim my LCD and other in-dash buttons with the regular dash dimmer knob!
As far as button interfaces go, that's about all ive got for now. I may end up with some sort of microcontroller solution for my buttons, but until I get that far... I wont really know..