Since 1924, no tool box has been complete without a pair of locking pliers, also known as vise-grip pliers. Locking pliers work like any other kind of pliers; they help you grip things. But locking pliers also allow you to tighten the jaws of the pliers around the object -- or whatever it is you're working on. By clamping the jaws into place you "lock" the pliers, and they won't slip.
Think outside the toolbox when using your locking pliers. Some people report using theirs as replacement shifters (both car and bike), as well as a battlefield surgical tool (sterilized, of course), and even as a kitchen tool to make removing hot pans or foods (even cannoli shells fresh from cooking in oil) a little easier -- and safer [sources: Sawyers, Irwin].