[quote="I use
http://www.kayak.com or sidestep.com and if the prices are too high and I'm within two weeks of departure, I put my itinerary up for bid at
http://www.compete4yourseat.com It actually came in $16.00 under the cheapest web airfare in December.[/quote]
You didn't say when your trip was, but if you're close to departure, try the compete4 website. Travel agents bid, and I usually get a lower quote. Usually they're good for that day.
Also, if you have some flexibility in travel dates, try expanding the kayak.com search to 3 days each side of your target date. Spirit dropped to $342.00 from $376.00 by going on a day before.