Extremely talkative five year old frightens off prospective friends

Hi Sara,We have a great but extremely talkative boy who will be 5 in June. He has a great vocabulary, but doesn't possess any natural shyness. When on elevators, in the store, no other child is safe from him chattering endlessly about his toys, likes or talents. Other kids often just stare, mouth agape, not knowing how or where to begin. He scares away potential friends, which scares me. I want him to be well-liked and know how to relate to others, as he will begin primary school in the Fall. How should I address this issue without squashing his exuberance?