WORD Sift is a site that allows you to paste in a passage of text and create a visualisation of the word frequency. Word Sift allows the user to click the word to feed a visual thesaurus.
Tagxedo turns words into a visually stunning tag cloud, words individually sized appropriately to highlight the frequencies of occurrence within the body of text.
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.