TagCloud is an automated Folksonomy tool to you make your own tag clouds.
Essentially, TagCloud searches any number of RSS feed you specify, extracts keywords from the content and lists them according to prevalence within the RSS feeds. Clicking on the tag’s link will display a list of all the article abstracts associated with that keyword.
The result is a list like this one below and you can use CSS to customize it. The popular keywords have larger fonts. This is the TagCloud of my blog RSS feeds:
(via Google Blogoscoped)