The Shopify PHP SDK by Tyler King is a simple, tested, API wrapper for Shopify using Guzzle that supports legacy apps. The SDK contains methods for generating an installation URL, an authorize URL, HMAC signature validation, allows for the checking of API call limits, and can make API requests through the use of Guzzle. It works with OAuth as well as private API apps.
Last month The New York Times released its own map mashup: Represent. This month the major media player has released a Best Sellers API, which provides developers with access to best sellers lists from several categories (view our new Times Best Sellers API profile).
When Zappos released its API, there was a strange restriction: no mobile applications. While sometimes lawyers write terms that aren't formally enforced, Zappos made it clear on its API mailing list that it was serious. Soon, the restriction will be removed and mobile applications will be allowed without written approval.