Stack Overflow, the very successful question and answer site for programmers, have now released their own API into public beta. The API actually works with all of the Stack Exchange sites, including serverfault.com and superuser.com, with more sites possibly launching in the future. The API is supported by the site http://stackapps.com.
At this year's SXSW, Mashery (a ProgrammableWeb sponsor) conducted a survey of attending developers and discovered something interesting: They care more about getting Commercial Terms of Service (TOS) than code samples from their APIs. Does this mean a new rash of coder/lawyers skewed the survey sample? No, it's just an indication that developers are growing up--and they expect their favorite APIs to grow with them.
For over a year developers have been asking for an API from Quora, the Q&A site that has recently exploded in popularity. The company had been waiting until there were "enough users and content on Quora." A browser extension outed the interface and now there is an officially released, but still alpha Quora API.