Plants of the Pacific Northwest Coast: Washington, Oregon, British Columbia & Alaska, Jim Pojar, A. MacKinnon, and Paul B. Alaback, Lone Pine Pub, Redmond, WA, 2004, 528 pgs.
This book was recommended by a number of my plant friends when I first arrived in Oregon. I needed some help to identify plants on my property and this book was just the thing. It comes in hardback, but I prefer the paperback version which is very durable and easy to take with me on hikes and travels.
The pictures in this book are very useful and include both flowers and foliage which helps with identification during the non-blooming periods. The book focuses on herbaceous flowering plants, but there are sections for trees, shrubs, ferns, and aquatics plants. Now that I'm rehabilitating a pond on my property, the aquatics section has been very handy. The book includes a notes section with information about historical uses or interesting lore about the a species which I really enjoy.