My little terrier pup pulls almost continually on a lead, even when standing still. Sometimes he'll walk nicely, sometimes he's an absolute pain. He also has a habit of lunging at people in the street, especially kids (just for a fuss, you understand).
This little gadget (I bought the small size) works a treat. No more pulling, and it stops him dead in his eagerness to 'greet' passers by. It's also less expensive than other makes, though with no sacrifice in quality.
Can't recommend it highly enough.