One of the most important--and too often forgotten--pieces of a successful API is promoting what developers have built. Doing so should be a win-win, as both platform and developer should benefit from third-party apps being discovered by users. Location-sharing service FourSquare just re-vamped its application gallery and now any developer can be included.
Exversion is hoping the need to access wide-ranging open datasets has matured enough to create a viable business as an open data marketplace. Their new Exversion API provides developers with a RESTful interface to search and access the open datasets stored on the Exversion data platform. At present, the API returns queries in JSON or XML format, with full XML support to be provided in the near future.