You can set up price alerts through sites like airfarewatchdog or kayak. They will alert you when the price drops with any airline, except southwest.
And you will usually find cheaper flights trying to fly on Tuesday, Wed or Thursday, either early, early morning flights or late night flights. So if you can rearrange your schedule to accomodate any of these, you may have better luck.
When I was looking for airfare, I checked the prices through kayak and southwest every morning. You just never know what day the prices are going to go down.
But, I'm going to be honest. Southwest, Delta, Frontier, Air Tran and Continental all just had great prices on their flights for late Dec, Jan & Feb toward the beginning-mid october. I'd be suprised if most people looking at that time frame didn't book then, decreasing the chance that they'll need to lower the prices in the future. I'm going over MLK weekend, the price before the sale was $176/pp each way and we paid $89/pp each way; the price now is $161, just to give you an idea of how much the prices have fluctuated and shot back up.