One of my favorite strength development tools is the sledgehammer.
The best way to use it is with two easy steps:
1) Get a heavy sledgehammer.
2) Hit something with it repeatedly.
Ross Enamait has an excellent and nearly exhaustive pair of articles on sledgehammer training.
A couple variations:
Rotational Chops - sideways swings.
Breaking Up Trash - Don't have a tire? You can smash up something that needs smashing.
Now all you need is a hammer...