Next time you buy a plane ticket, use Farecast, a Seattle-based company that has reverse-engineered the algorithms used by the airlines to compute plane ticket prices. Is it better to buy today or wait until next week? Farecast tells you the answer. I've been blogging about these guys since they were beta, but they've come a long way since then.
For example, they now have a way to lock in a fare without buying the ticket. If you pay them $10 (or $3 during their current special deal), they will guarantee for one week whatever lowest price you find today.
For example, suppose I want to fly my parents here to Seattle to visit me sometime in the next several months. According to Farecast, the lowest price is $257 if they leave on the afternoon of Feb 6th or 7th. The next lowest price is $309. Imagine if I had tried to find this fare the old-fashioned way, plugging in various dates one after another.
Another way to search is by destination. Where are all the cities I can fly to for less than $200 on my birthday? Who would have guessed that I can go to New Orleans? Or Philadelphia? Plenty of restrictions apply (I have to leave Tuesday and return Saturday), but hey, a deal is a deal!