What data/functionality would you want to have available through a web API that isn't available today?

Have you ever looked for a web API for certain data or functionality, only to find that there isn't an API available to meet your needs, or that the APIs that are available are inadequate for some reason? I am really interested in collecting such experiences.

Please note that I am not asking about specific sites / web apps (so, for example开发者_开发技巧, "I wish there was an API for CraigsList" or "I wish there was an API for Orbitz" are not appropriate answers). But what I am asking about is specific data/functionality (for example, "I wish there was an API to retrieve historical stock quotes for Asian markets" or "I wish there were better APIs that allow me to send a fax to a physical fax machine" would be good answers).

Bonus points if you provide some detail on how you would use the data/functionality that you're looking for, and if you can say whether you would pay for access to such an API or not. Thanks!

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More (easier?) accessibility to consume government accounting and spending. People have compiled lists of the available APIs but things are still all over the place. This poster is and awesome start. The nerds of the world could really have a field day with data sets that large.