Wired posts a simple method for finding south using nothing but an analog wristwatch and the sun:
Hold a watch with 12 o'clock at left. Move your arm so the hour hand points at the sun. The spot halfway between the hour hand and the 12 is north.
The comments of the Wired post offer a few important caveats. First, if you're in the northern hemisphere, you would point 12 o'clock at the sun but still split the difference between 12 and the hour hand for south. Also, if you practice daylight saving time, you should subtract one hour from the hour hand.
The former Boy Scouts and Girl Guides out there may say 'well duh!' but this one's handy for the rest of us.