The Developer Tutorials blog has posted a tutorial showing you how to set up a tag cloud for your site:

Every major website seems to have a tag cloud. Users love tag clouds; they help navigate masses of content quickly and easily. [...] How do we actually build a tag cloud at application level? In this tutorial, I'll take you through putting together a full-blown, calculated web 2.0 tag cloud in PHP.

They start at the end, with an example cloud with some sample tags ("php" being the largest, of course). The code for it is pretty simple - it looks at an array of counts, the number of times the tag is used, and builds the links with the correct font size automatically.

For the Oracle users out there looking for an easy way to pull those tags together and make a handy little cloud out of them, Maggie Nelson has posted about a simple Oracle function that can help - NTILE.

For example, check out the documentation for the NTILE Function. Yeah, sounds kind of boring. What good could it be in the wonderful world of web development? After all, who manages employee or sales tables anymore... Answer: generating tag clouds.

Her SQL statement categorizes the tags for you automatically, dropping them in to "buckets" of font sizes. This makes it simple to loop through them (like with a foreach) and output your tags with a little help from some CSS. You can even specify how many buckets you want it to fill (how many different tag values to get and compare).