One of my grandmothers swears by cutting onions under running water. The other recommends lighting a candle with a scent heavy enough to overwhelm onion vapors. Neither trick--or any other old wives' tale, for that matter--has prevented me from tearing up whenever I'm slicing onions. But RSVP's Onion Goggles seem to do the job, without resorting to any unusual tricks.
Goggles and contact lenses have been proven fairly effective in reducing or preventing tears while you cut onions. The Onion Goggles use a comfortable foam to create a seal that protects your eyes from onion vapors, along with antifog lenses that won't interfere with keeping your fingers out of the way of the knife. The goggles also come with a storage case to help keep them clean. The only drawback I've found is that the Onion Goggles don't really fit over regular eyeglasses--chemistry lab goggles may do the trick, although they won't look quite as nice as the Onion Goggles.
Onion Goggles are available in a variety of colors, but the pink set is associated with the Breast Cancer Foundation, which will receive a portion of all proceeds. The goggles are priced at $19.99.