One thing that I've read and heard from various travel experts (on TV, magazines, etc) is that most fares will drop (if they're going to be dropping) on Tuesday night (Wednesday AM) sometime after midnight.
I'm always checking for airfare from somewhere, but that "theory" proved very correct twice a month ago. I had been checking daily, and on Wednesday morning when I woke up fare from PIT had dropped to $98. By the weekend it was up to over $250, and on the following Wed (after we had another person decide last minute to go) the fare dropped again, down to $115. Both of those were sometime in the middle of the night Tuesday into Wednesday just like all those "experts" said!
Carrie