Passport to Web 2.0

http://www.wordle.net/
Wordle is a toy for generating “word clouds” from text that you provide. The clouds give greater prominence to words that appear more frequently in the source text. You can tweak your clouds with different fonts, layouts, and color schemes. The images you create with Wordle are yours to use however you like. You can [...]

 
Add a tag cloud to any site.
Tag Cloud from an RSS Feed
Make a tag cloud from any RSS feed, then add it to your blog or site
Tag Cloud Widget
Turn your favorite RSS feeds into a tag cloud widget for Netvibes, iGoogle, Dashboard, or Opera.
Tag Cloud from Search
Generate a tag cloud based on a search [...]

TagCrowd is a web application for visualizing word frequencies in any user-supplied text by creating what is popularly known as a tag cloud or text cloud.
Today, text clouds are primarily used for navigation and visualization on Web 2.0 sites that employ user-generated metadata (tags) as a categorization scheme.
 
Features and uses

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as topic summaries for speeches and [...]