The Facebook SDK for PHP enables developers to access the Facebook Graph API and use the Facebook Login from within PHP applications. Examples are provided that show how to use the SDK to retrieve a user's profile, post a link to a user's feed, and upload a photo to a user's profile.
Something new sprang up in the Flickr App Garden last month: "This is my Cam!" by Chris Martin (the San Francisco-based hacker, not that guy from Coldplay). Inspired by music sharing site This Is My Jam and built during Photo Hack Day 3, "This is my Cam!" uses the Flickr API to catalog the different cameras that were used to capture a particular user's photos.
Magnify.net, a web service that allows individuals and companies to build and curate their own video channels and communities, has announced an API to enable developers to pull videos and data from their Magnify.net channels and integrate them into their own applications (details at our Magnify.net API Profile).