I use this from REI.

You can buy a separate laptop sleeve that hooks in and suspends it so that it isn't hitting the bottom of the bag. I usually throw my extra t-shirt and socks in underneath it for padding. It is also just an all-around nice bag for biking. It has a rain cover stashed in a pocket, is very comfortable, and the right # of pockets. Just a bit small.

I used to use just a "regular" backpack. I'd have a similar placement strategy... some socks/t's/underwear beneath it, my back against it, and pants/shirt between it and the outside of the backpack. I figure I'd have to land in a really weird way to hit it bad on the ground. I suppose a car would not be good for it (or me).