For those of you who haven't already heard (I just learned about this), there is an application for your phone called Hopper. You put in your proposed flight route/dates, and this application will tell you what the range of costs are and when you should buy your flight to get the lowest cost. It will send you a notification if your flight cost is going to rise so that you can grab the flight before that happens. It's pretty cool. One limitation, though, is that it doesn't search American Airlines.