WordItOut (13+, Parent permission required if under 13, high)
WordItOut An attractive arrangement of randomly positioned words, where the most important words are bigger than the others. They are fantastic at summarising large documents (reports, speeches, questionnaires, etc), teaching kids and more. You can type in your words, sentences or paragraphs. You can also copy and paste documents and reports.
WordItOut allows users to make word clouds. Saving and downloading the clouds does require an email address, so this would work best for students with email account.
Some classroom applications include brainstorming to see what words come up most often, or maybe having students copy a report and paste it into the text box to see if there are overused words involved in the text. Teachers can copy and paste verbage from content text to give a review for exams.
Here is one example: http://worditout.com/word-cloud/42623