When I was buying our tickets they seemed to be less expensive in the middle of the week and then would go up again on the weekend. I noticed that over a few weeks span. I wound up purchasing them on a Wednesday and got the best fare I have seen so far. I'm not sure if that was a fluke or the way it usually works, but it saved us several hundred dollars.
My suitcase is out and the cool weather clothes are starting to go in it.....not that I'm excited or anything :-)