Fare Compare
Update: Fare Compare killed a lot of their neat feeds. ExpertFlyer and Google Flights seem to be the way to go now.
I was reading through the Upgrade Travel blog and found a mention of this nifty thing called Fare Compare. It’s great because not only does it show really good rates and historical trending information, but it also helps you find discount First Class fares. I wish I’d known about this thing a few weeks ago.