FareCast is a site devoted to when you should buy a plane ticket to get the best deal. According to their website:
We use data-mining algorithms to search for patterns, in the accumulated airfare data, which are associated with significant price changes. These patterns are represented and stored in models, and the models are then rigorously trained. Once created and trained, we use these models to predict the future. Then, new, current airfares can be scored by the model to answer the question, "is the price going up or down in the future?"It's a limited beta right now that only works with flights originating or arriving at Boston, MA or Seattle, WA.
Keep an eye on this. This could be a very useful tool as they add more cities to the search.
Link (via Boing Boing)