I have to share this link with you about how you can track airline fares using Yapta.com First of all, Yapta will tell you if you can get a refund for the difference if you paid a high price for an airfare. Most importantly, use it in advance of buying a ticket to alert you to when there are price drops. The NY Times did a great feature about how to save $$ on your next trip. http://www.nytimes.com/2011/01/09/travel/09pracsave.html
I wish I had this when I paid $760 for my last ticket to Oaxaca and another $900 for a second ticket. Dern it.