I completely agree with any books from Michael Dirr. He has a bunch of books out with both photos and information.
A couple more I would like to recommend are from Tracy DiSabato-Aust. She has written The Well Tended Perennial Garden and The Well Designed Mixed Border. Good stuff...and not really written for the homeowners. The Perennial book gets into soil sciences and tips to manipulate perennial bloom times and growth habits. I have recommended them to clients and they were a little over their heads.
Cristin M. Larson, The Garden Consultant
Rhode Island Nursery and Landscape Association - Member and 2009 President