I found this great website last night.
www.farecompare.com
It gives historical data for the past two years on ticket prices.
For example, I am watching for tickets to LA from Buffalo. On that site I enter the cities I'm traveling to and from and it shows a graph with how low and high rates have gone btwn BUF and LAX in the past two years.
I also like
www.airfarewatchdog.com for watching ticket prices. I live in Buffalo and I keep seeing tickets to Orlando for about $125 (American) r/t. I haven't paid attention to the dates though.