I am going out to LA next week for the Adobe MAX conference. I wanted Terra to come out for a few day but it looks like that is not going to happen. In the process of looking for flights I found a great site for comparing flights for a few months at a time. You select the departure city and starting month, then a arrival city and a ending month. It creates a nice graph that shows you each day between your start and end date. You roll over the days to see the price.
The site really is just a shell to search all the airline to get the cheapest and fastest flight. It works well and is super easy to do compared to Expedia and some of the the other major online travel sites.
Here is a screen shot of flights from Chicago to Dublin, Ireland from Jan to Feb 2010.
Check the site out for yourself at http://www.functravel.com/.

