Lineman's Pliers
Most folks have one of these pliers in their toolbox, but don't know they are called Lineman's Pliers. The name comes from the fact that the guys who work on the power lines use them. They are  heavy duty gripping pliers with both flat and cirular sets of teeth for grabbing heavy cable. They also have a cutter. I use them for a strong grip on my metal pieces and a sturdy holder for bending tough material. They are available at any hardware store and come in many different sizes. Click the picture for more information on this very versitile tool.