I agree with Tessa. Somewhere on here Dr2little has recommended a very good sounding harness which prevents pulling with none of the physical or psychological risk of damage...probably what Tessa was talking about. I forget the name.
The two options that I like best (but again are still only for temporary control, not training) are the Halti brand no pull harness with the leash attachment on the front and the newtrix easyway collar (newtrix.ca). I absolutely agree with Doberluv with respect to the Gentle leader and Halti head collars, the Newtrix has a totally different design. It is still a head collar and does go over the muzzle and head but because it works on oposition reflex and the leash attaches to both the regular collar and the back of the head collar, the muzzle part is much more comfortable without the risks associated with the chin control designs (halti and gentle leader). As with any new tool, habituation has to be done slowly, with tons of praise and patience and no device should ever be used on a walk until the dog is clearly comfortable wearing it. I always recommend that my clients put the new tool on, for only a few minutes each time and pair it with fun things such as games, toys and treats and only remove it when the dog is not fussing with it. This should happen several times a day for as many days as it takes to see the dog get totally excited when he sees the head collar.
Like Doverluv say's, these tools for some dog's may mean the difference between no walks and many walks so in those cases I'm all for them. Also, I have some clients who's dogs far outweigh them and these tools can ensure safety for all especially in the social enviornment of today where dog/public safety is such a hot button. Train, train, train...and if you must use a control tool these are some that are kind, gentle and very effective.