Dr. Patricia McConnell is a leader in the field of dog training and behavior. Her books - mostly written for dog owners - range from general information to guidance on more specific training issues (reactivity, house-training, shyness, etc).
Dr. Ian Dunbar is often credited with being the father of "puppy kindergarten" classes - before him, most training classes were geared toward owners of adult dogs who needed help with problem behaviors. His work is an amazing resource for puppy parents - particularly Before and After Getting Your Puppy.
Jean Donaldson is an author and trainer who runs a school for dog trainers, and whose books and blog give incredible insights and guidance for understanding and communicating with your dog.