John Battelle delivered the web platform story of the day yesterday by reporting Amazon will make Alexa's 5 billion web documents and 100 terabytes of data available via the Amazon Web Services Platform. See his story for some interesting possibilities and there's also a good summary at Wired.
There is a (reasonable) fee for using this data: The first 10,000 requests per month are free. Thereafter, requests are charged at a rate of $.00015 each (just 15 cents per thousand requests.). For example, if you make 100,000 requests to the Alexa Web Information Service during a given month, you will be charged $13.50.
This announcement leads Phil Wainewright to ask good questions about funding API services with advertising and what are Google's core competencies.
One example application using Alexa is Musipedia search which gives you the ability to search the web by melody (entering a keyword or melodic contour returns similar music).