VocabGrabber analyzes any text you're interested in, generating lists of the most useful vocabulary words and showing you how those words are used in context. Just copy text from a document and paste it into the box, and then click on the "Grab Vocabulary!" button. VocabGrabber will automatically create a list of vocabulary from your text, which you can then sort, filter, and save.
Check it out: http://www.visualthesaurus.com/vocabgrabber/
and try your hand at the "Spelling Bee" - http://www.visualthesaurus.com/bee/