Sometimes it's all about the gear. One of the best solutions for dogs who pull is a front-connecting body harness. The best on the market are the Halti and the Sensation.
The key to success with both of these harnesses is that the leash is attached to a ring on the chest. Why is that important? Because it's the dog's center of gravity. Uses? These harnesses are great for small people with big dogs, dogs with neck injuries, and dogs for whom nothing else works (including head harnesses like gentle leaders).
A body harness does not replace proper dog training. If you do not have a positive dog trainer in your life, contact me or find one in your geographic area through the Association of Pet Dog Trainers.