WikiMindMap makes use of Wikipedia to generate a mind map of the search term. I've used Changi as an example in the screenshot above. Students shouldn't be using Wikipedia as a primary source. Nevertheless, that doesn't detract from WikiMindMap's nice way of displaying the entry's related terms.
Click on the words on the branches to go to the actual Wikipedia entry. Click the 'recycle' logo to bring that term to the center of the mind map.
Hat tip to Ewan McIntosh.