You need to change his emotional response to seeing other dogs. Do not use anything adversive such as tugging on the leash, spraying water in the face etc when he sees another dog. He will just associate the dog with that. Here are a couple of videos on a positive way to change his response.

http://www.youtube.com/user/pamelama.../0/uFiZkAG_1JE

http://www.youtube.com/user/kikopup#p/u/51/JY7JrteQBOQ

I would highly suggest trying to find a class for reactive dogs that uses positive reinforcement and attending it with him. Good luck!