SmartWool is a company that specializes in creating 100% merino wool activewear. They are actively encouraging the ethical treatment of sheep — see this previous post for details on their attempts to end "mulesing". These socks from Smartwool are made of 73% merino wool (the rest is nylon and elastic). The sock's fibers will pull moisture away from the foot keeping it dry. You can also wash and dry this sock in a machine and it will not shrink. Available for $12.76 from ProLiteGear.