buy on wed or thurs...
the prices go up and down throughout the week. watch them...

and go to kayak.com

You might find a better fare to Portland or Vancouver or Eugene or Spokane. There are buses and trains between Seattle and all those cities. Look into other possibilities, such as travelling by land to a hub that isn't unbearably distant and flying from there. Continental has (or had) non-stops from Houston that could offer a better deal. These all take more time and a deal of work but just as time is money, money is time.

My "secret" is to plan well ahead and buy when I see a fare that I consider reasonable. I don't try to save the last cent and I quit worrying about whether someone else might have got the same flight for twenty or thirty dollars less. When the budget just won't reach an unreachable fare, I start looking into the air/land combinations I described.