Wordnik is a project devoted to discovering all the words and everything about them to show you as much information as possible: “an example sentence, images from Flickr, statistics, audio pronunciation”. There's also a thesaurus-plus "related words" feature, which shows not only synonyms and antonyms, but other words that are used in a similar context. Wordnik collected more than 4 billion words of text (web pages, books, magazines, newspapers, etc.), and more than 130 million examples! to show you example sentences for any word you're interested in.

More info: Wordnik