This is a really interesting article about the state (hint: sucky) of the online travel industry.

http://www.tnooz.com/2013/06/05/news/the-state-of-some-travel-startups-and-why-some-are-missing-the-pain-point/

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.)