This is a really interesting article about the state (hint: sucky) of the online travel industry.
While I don't actually agree with the recommendations - starting a little startup and trying to get Expedia to link to you is basically a cop-out that will fail to solve the underlying problems - the problem statement is pretty clear. Multi-modal is where it's at. There are some great examples of what would be possible if that really worked. (For example, estimating the total cost of choosing a more remote airport (longer taxi ride) to save money on flights.)