The Marmot Driclime was one of the original windshirts. Mine is several years old and still works. However, it doesn't have a hood, or pockets, like the one I have linked to. Since this was in a sale, I couldn't resist buying it:) The inner is a microfleece and the outer is Pertex. It's not waterproof, but it is water resistant. In anything other than a torrential downpour, it will keep you dry provided you keep moving and generating body heat.
The Pertex outer is very wind resistant. If it's breezy and you are feeling the chill, just stick this jacket on and you will be instantly warm. It's very light and can be rolled up into its own chest pocket, taking up very little space.