This package can be used to generate tag clouds. The output is HTML and CSS.
And it does not only visualize frequency, but also timeline information.
The newer the tag is, the deeper its color will be; older tags will have
a lighter color.The main goal of "HTML_TagCloud" is to provide an easy to
implement and configureable Tag Cloud solution that is suitable for any
PHP-based webapp.

WWW: http://pear.php.net/package/HTML_TagCloud/