Have a device installed right in a car that can detect tire pressure and re-inflate them automatically using the engine's power. I thought of this this morning in the Driver's Ed classroom (which is all done now, finally) when I heard the teacher saying something about the engine stabilizing pressure. He was referring to the oil chamber or something like that, but I couldn't help but wonder why this couldn't work with tires as well.
Even if this wasn't an automatic system – you'd have to check yourself then get the engine to fill the tires – it would still be really useful. In an age of rising fuel costs, it makes sense to have your car running as efficiently as possible.