By using Yapta.
I can't wait until I get a chance to use this! I only wish I had found it before the holidays. The scoop? You put your flight plans into Yapta.com and they watch the flights for you, alerting you when the prices drop.
So then you buy your tickets, and the next day, the price drops again. Don't be distraught! Yapta gets you a voucher or refund from the airline. Can it get better than this? I submit that it cannot!