Woolrich has come out with an excellent blanket for all types of outdoor uses. It's called the Travel Blanket. One side is nylon and the other fleece. I've had the chance to test one out and I have to admit, it's great. Now if I can only get it back from my wife!
Here is what it looks like both folded up and unfolded:
If you're interested in one (or two) you can order them here.