Word of mouth is a powerful marketing tool, and businesses (not to mention the consumers), can benefit greatly from helpful reviews. Popyoular is an editorial review-based recommendation and discovery platform. It's aimed specifically at film, music, books and games. The idea is to connect a website's good content with trusted reviews and opinions about that content, helping to keep users engaged and directing them to things they may otherwise have overlooked. Popyoular's API makes it possible for developers to integrate this functionality into any other website.
SEOmoz recently provided an API to their search engine optimization service, and inevitably comparisons were made to Site Explorer, which is a similar service offered by Yahoo. In a field where stats are king, the 500 links offered by the free SEOmoz service seemed to come up short against the 1000 links offered by Site Explorer. That has now changed, with SEOmoz doubling their volume of data available with their free API.