Yapta.com
I recently stumbled upon this gem of a site.
It’s a neat web app that tracks price fluctuation for all kinds of flights. You can search for flights in a similar interface to expedia.com and once you find a desirable flight you can add it to your “Trips”.
The “My Trips” section is a list of all your planned trips (nicely designed too boot). Once you’ve planned a trip Yapta tracks the ticket price over time and keeps a running chart of the price fluctuation. Yapta also emails you when the price drops. You can purchase the ticket through yapta once the price looks good for you. If you do happen to buy your ticket through yapta and the price drops after the fact, they will help you get a rebate through the airline.
I only wish I had found out about Yapta before I booked my flights through expedia.com and signed a life long contract with Continental because they were the only airline at the time of purchase that had tickets to California for under 500 bucks. Check out Yapta!