I got my tickets for my Christmas trip to Nebraska last night, and I saved a couple hundred bucks over what I usually pay. Bing Travel has a couple neat features that worked out pretty well for me: you can get an RSS feed of a particular itinerary and easily track when prices change, and it will predict whether prices are likely to go up or go down from where they are. I hadn't realized how much the prices of flights fluctuate until a couple weeks ago. A flight that I usually end up paying $600-700 for dipped down to the $500s a couple weeks ago, and for a moment last night dropped down to about $365. By the time I was able to complete a purchase the price was up to the low $400s, but still, that's a pretty significant savings over what I usually pay. In fact, it's roughly the price I was going to have to pay on top of using 35,000 reward points on my credit card, which are themselves worth about $300.
Now that I know how much prices can fluctuate, in the future I'll have to remember to be more patient and vigilant when buying flights.