I had the same problem, use the Dog Whisperer method:
Short leash attached directly to tightly affixed collar. Works great.
When they start pulling or looking around at other dogs etc, just make a quick sound and jerk to re-focus them.
I started out with a harness and after a few weeks of my 1.5 yr old pulling me all over the place I tried this method, I haven't had a problem since.
Watch the show too, he shows people how to do it on their as well.