The Big Huge Thesaurus API provides a convenient interface for initiating a search based on an English word and retrieving related words and phrases.
The Big Huge Thesaurus includes more than 145,000 english language words.
GoodGuide is a service that we have been using as a family for a while. It attempts to analyze a product holistically & scientifically to produce a simple 1 to 10 rating of its "goodness." I am personally satisfied to see that the GoodGuide API will share this data with the world.