Secret #1: There's a pattern to how fares rise and fall.
Based on 250 factors that have an impact on ticket prices, Farecast.com  spits out a prediction about a proposed itinerary. If fares are trending up, you are advised to buy. If the site predicts a coming fare drop, it suggests that you wait. You can also purchase a FareGuard guarantee for $9.95. Then, if the price spikes a week after you were told to sit tight, it will send you a check for the difference. Farecast's clean interface and snappy graphics, such as its 90-day price-history graph and multicolored predictive arrows, make it the easiest of these new services to use.
Secret #2: You can fly first class while paying coach prices.
FareCompare.com's  "First Class Search" button scours its database of airfares for a little-known option called the Y-Up fare. These are tickets coded for coach, but they get you seated in the first-class cabin. While not cheap, they are great for business travelers because they cost much less than a full-fare first-class ticket and often will beat last-minute full-fare coach tickets--not to mention getting around that "no first-class travel" rule in the corporate handbook. Overall, FareCompare has much more data than Farecast (for example, it serves up 30 months of historical fare data, versus 90 days), but its confusing interface makes it recommended only for extras like Y-Up and its nifty map of cheap fares from your local airport.
Secret #3: The airlines will pay the difference on fare drops.
Yapta.com  (an acronym for "your amazing personal travel assistant") is designed to let you take advantage of underused regulations called "guaranteed airfare rules." If the price drops on the exact class of fare that you purchased, the airline owes you either a refund for the difference or a voucher for future use. Yapta makes it easy to tag a flight (much the way the article-tagging application del.icio.us works), and it alerts you if you meet the criteria. It's also incredibly useful before you buy. Download Yapta's browser add-on and each time you're on a travel site, the Yapta Tagger button appears next to the flight. Clicking it adds that info to your portfolio. Set a target price, and Yapta notifies you when it's met, so you can buy before it jumps again.