I have two pairs of sunglasses that I wear for driving.
My favourite for strictly driving are these "Matrix" Agent glasses from the 1st movie (black pair seen below). They cover the eye completely, so no light leaks in around the edges. The image is clear and the UV protection is superb:
The other is a DKNY model that I use as my daily use pair. I'll just keep on if I happen to be wearing them when getting in the car. I had to replace the lenses as they got scratched. I'm not as happy with them as the polarization causes LCD displays to be almost unreadable but they cut reflected glare from transparent or near transparent surfaces quite nicely.