The Stipple API is free, has no request limits as of yet, and OAUTH 2 will be supported in the future. According to its website on the API, it is "inspired by REST". Stipple announces its rare downtime, which is usually used to migrate data, via its twitter account.
Skybiometry's cloud-based face detection API serves as a drop-in replacement for face.com's API. This REST-based API can be used in combination with almost any programming language, making it possible to integrate with any device that has internet connectivity.