Christine Donahue, and collaborators Clint Nelson, Dan Reed and Shannon Harrer, have come up with a great field guide to locally common plants and animals. To me, the best aspects of this guide are the algae and inverts. It resolved a lot of the doubts and questions I have about those plants and animals that you see everywhere on the bottom, and seem to take a few different forms that may be related. Like, what are those big single-bladed algae that look like laminaria, but are completely smooth and have a central rib? (They are young sea palms). It distinguishes between coastal and island environments: which are pof course retty different. And, it's free for the downloading:
http://sbcdata.lternet.edu/external/Documents/Publications/FieldGuide.pdf