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