What APIs do you wish existed?
dlg: - US & State Government tax information.  The tax code is amazingly complex.  It would be good if you could figure out the tax implications of various events.  Better if they simplified the tax code to where this was possible.
   Moreover, data.gov so far is a disappointment.  Maybe they'll improve it.  But I'd love to dig in to purchasing and personnel costs for every branch of government.- Good stock market historical tick data (and streaming data).  Opentick tried for a time, but mostly you need to contact expensive services.  This makes it hard to mess around.- A good local event API.  Lots of companies have tried, few have good results.- LinkedIn: They've been promising an open contact book API since 2007, but have kept it closed.  If they had an open API (that lets you actually store data/invite), it would mean a lot of sites would be building on them.- My dream: The big scientific journals would require everyone publishing a paper to upload all relevant datasets to a central repository which could be queried.- Anyone you have an account with (Financial firms, banks, vendors) would have a standard commerce API.  Sure, today you can export stuff in Quicken, etc formats, but Mint had to do a big deal with Yodlee to get the data in a uniform, queryable way.And, mad props to Microsoft for opening the Bing API with pretty good terms.  Google used to have a search API and it had horrible terms.  Then they decommissioned it.  Who would have guessed that MS would be more developer-friendly than G?