Bear Hug: A man once escaped a bear attack when he locked his arms and legs around the bear in a reverse bear hug, which made it confused and it ran off. If you're on your back and the bear is on you, it might be your last resort.
Gag Reflex: Bears, like many animals, have poor gag reflexes. A man recently survived a vicious bear attack by shoving his arm down the bear's throat, causing it to gag and then retreat.
Eye Gouge: Big bear has you down and is seconds away from having you for dinner. If you have a free hand left, drive a finger into the eye. Blindness ends all excursions.
Play Dead: Okay, this doesn't work when a bear has stalked and attacked you, but will work with bears protecting their cubs or territory. So if you are a lover, not a fighter, play dead.
Pepper Spray: Mace, pepper spray, wildlife repellent... they are all great at making a bear retreat. If you don't have any with you, read the other steps listed here.