I agree with the baby shampoo, makes their coat lovely and soft I also like companion aloe vera shampoo, as its designed for frequent use (doesn't affect ph/ oils etc) and when my JRT was a puppy she would regularly roll in something smelly!!
I like P@H teatree one. Started using it when he was a bit itchy last summer makes him beautifully soft a "clean" smelling rather than "girlie" smelling!
I use my horses shampoo on Ruby but it is meant for dogs as well not cheap mind you but leaves her smelling gorgeous and soft and you dont have to use much. Called Megatek i think...