Using even the simplest of radio setups and antennas, amateurs communicate with each other for fun, during emergencies, and even in contests. They handle messages for police and other public service organizations during all kinds of emergencies including hurricanes, earthquakes, tornadoes and floods, motorist accidents, fires and chemical spills, and search and rescues. They help organize parades and other local events... the list goes on and on.

The above was adapted from "Hello Radio" on the ARRL web site. Give them a visit... there's lots of interesting stuff there.