Recommended reading:
• Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions, by Arthur M. Shapiro and Timothy D. Manolis (order this book from Amazon.com).
• Butterflies through Binoculars: the West, by Jeffrey Glassberg (order this book from Amazon.com). A new favorite, this book has very good photos, plus loads of information about butterfly behavior. For example, the author advises looking for anise swallowtails on hilltops (once I read this I had a major "of course" moment, since everytime I've seen anise swallowtails, they've been on top of hills).
• Common Butterflies of California, by Bob Stewart (order this book from Amazon.com). Beautiful photos, and a good source for bay area butterfly identification.
• An Obsession with Butterflies, by Ahrman Apt Russell (order this book from Amazon.com). A sweet little book packed with little tidbits about butterflies and moths. I particularly enjoyed reading about butterfly behavior, including how butterflies find host plants: they look for familiar leaves, then land on contenders and "taste" the leaves with their feet.
Links:
Butterflies and Moths of North America http://www.butterfliesandmoths.org/