If you're paranoid, fill up the gas tank, disconnect the negative terminal, and put your car up on jack stands to avoid flatspotting your tires. This, of course, is at your home and not an airport garage. I would never leave my car sitting unattended in a public spot for a month.
Disconnecting the battery is good advice. First, it will prevent the average idiot from stealing your car (most won't spend the time to see if the battery is connected), and second it increases the chances that the battery won't die while you are gone.