The recent Grist article "Helmet Wars: A gripping account of the great bicycle helmet campaigns" begins to explore some of the sides of this issue, and provides a number of links to excellent resources on both sides. Check it out, and tell us where you land on the helmet issue.
Whether you think bicyclists should or shouldn't wear helmets, make sure to follow the law in your area. Washington has spotty mandatory helmet laws, which vary by region. Check this WSDOT list if you aren't sure whether you're in a mandatory helmet region or not. And if helmets strike you as oh-so-uncool, you can always follow Momentum Magazine's instructions for how to turn your helmet into two different kinds of mohawks (zip tie or fuzzy).