There are a couple of free (as in beer) programs that can help you draw up wiring diagrams or schematics. Some of them will even turn them into PCB templates for you. These are the ones I've used:
Fritzing: Fritzing is designed to work with Arduino systems, but is still very much in alpha. Still, I use it for quick and simple schematics of my Arduino projects as it has most of the wiring all set to go.
Eagle: This is the program most serious people seem to be using. I find its interface to be extraordinarily complex and non-intuitive. There's a free version with just a few limitations, or pay for the real version with none. Can export to PCB templates.
Any suggestions on other alternatives? I'm a Mac user, so I only listed the Mac-compatible ones here. I know that other folks use ExpressPCB and some other programs that are Win-only.