This elegant online tool allows you to input a handful of values to generate involute gears of various sizes and teeth. Most likely, you will want to check the "Two gears" checkbox and punch in the gear ratio (as number of teeth). You can then check that the values will create a gear pair that won't jam by checking the "Animate" checkbox. If you see the teeth of one gear overlapping the teeth of the second, you need make some adjustments.
This tool uses printer-friendly Flash. Use the on-screen "Print gears" button to print out only the gears and not the entire web page.
He even shows how to cut the wooden gears on the bandsaw.
Generate some gears to cut from wood using the Interactive Gear Template Generator. [via Make Magazine's blog]