Power hammers are a great addition to any blacksmithing shop. They can hit your workpiece harder and faster than you can and leave you free to concentrate on positioning the metal for exactly the strike desired. Have a look at a few examples of this great tool here:

My home made hammer!! by John Perks


My mini power hammer by tlimknives


An in-depth look at Gunnhilda, my homemade power hammer by Helmforge


Norm Tucker's power hammer by yekitizer


Homemade power hammer by David Whiting


100# power hammer by Sander Vercammen