If you want to train a dog you already have, check with your local Humane Society. Some of them have programs to help train assistance dogs.

Websites:

• American Dog Trainer's Network: Service & Assistance Dogs
• Assistance Dog Information
• Assistance Dogs International
• Canine Academy
• Canine Companions For Independence 
• Dogs for the Deaf
• Fidos For Freedom
• Florida Dog Guides For The Deaf
• Fuzzy Faces' Cool Links - Service Dogs
• Hearing Dogs for Deaf People (in UK)
• Hearing Dogs for Deaf People New Zealand
• International Hearing Dog
• Introducing Dennis Robertson and Crackers the Hearing Dog!
• Partner's For Life: A Service Dog's Tale - a 7˝-minute video that portrays service dogs and their partners in real-life situations. It's goal—to educate employees in all commercial areas such as airlines, hotels, land transportation, restaurants, grocery and retail stores, as well as all types of government and educational institutions.
• Paws With A Cause®
• Sam Simon Foundation
• Texas Hearing and Service Dogs
• Top Dog - Dedicated to teaching people with physical disabilities how to train their own dogs to become fully certified service dogs.
• WOLF PACKS® ~ Gear for Working Dogs

Books:

• Animals with Jobs - Hearing Dogs (Board book) by Judith Presnall. ISBN: 0737718269. Reading level: Ages 9-12. Making physical contact with their paws or noses, hearing dogs alert their deaf or hard-of-hearing masters to ordinary household noises. These sounds include doorbells, alarm clocks, ringing telephones, buzzing oven timers, blaring smoke alarms and even crying babies.
• Lend Me an Ear: The Temperament, Selection, and Training of the Hearing Dog by Martha Hoffman, Mark Anderson. ISBN: 0944875564. From The "Partners Forum" The magazine of the International Association of Assistance Dog Partners. Lend Me An Ear by Martha Hoffman breaks new ground and would be an outstanding addition to the library of anyone with an interest in the assistance dog field. This trainer who is affiliated with the San Francisco SPCA Hearing Dog Program has evaluated hundreds of shelter dogs over the years. She believes hearing dogs are born, not made. She discusses what what evaluation tests she administers in what order and how to interpret the behavior each candidate displays. 
• Luke And His Hearing-Ear Dog by Andrea J. Zoll and Arlene J. Garcia. ISBN: 1412018153. Reading level: Ages 9-12. Adventures happen when Luke, who is deaf, gets a puppy named Herald. They discover they can talk to each other, and together they learn about friendship, love and trust.
• Sound Friendships: The Story of Willa and Her Hearing Dog by Elizabeth Yates. ISBN: 0890846502. Sound Friendships is the story of Willa Macy, who lost her hearing when she was fourteen years old, and Honey, a golden retriever, who helped her to discover a new world of independence and security. It is also a story about Hearing Dogs--their background, training, special abilities, and the unique relationship they develop with their owners in working to surmount the barriers of a physical handicap.