Haven't seen this linked yet but just picked it up today.
Logitech Cordless Mediaboard
It's made for the PS3, but I just plugged it into my Mac mini and it works perfectly save the lack of an apple or Windows button. It is a full size board with laptop style keys, very thin. There are also two keys on the bottom left to act as left and right mouse in addition to the two buttons below the trackpad.
Picked it up from Target for $70 in the PS3 accessory section. Hope this helps, my mini isn't installed yet so I don't know the range in the car, will post about that later.