“Jerome’s Keywords” is a plugin for WordPress 1.5.x and 2.0 and to associate keywords with your posts.

I used it for my tags on the right. To get them to look like a cloud, I used the following code:

<?php all_keywords('<strong><a href="/tag/%keylink%" style="font-size: %count%px" >%keyword%</a></strong>', '', 10, 30) ?>

Jerome’s Keywords Plugin>>