Make sure to check out www.farecompare.com
You can check fares from different airlines and receive insider tips on booking travel. It is updated periodically and it is very user friendly. It uses a calendar format to show you the low fare days you are looking for which is fantastic!
I highly recommend this site. I have not booked travel on it yet but the searches are excellent! Also, make sure to compare coach class and first class fares because a little birdie told me that first class really isn't a whole lot more expensive and you can compare on Fare Compare!