singpolyma

<ul>
<li>Detects tags from search engines, wikis, or other blogs</li>
<li>Auto-expands detected tags</li>
<li>Shows related posts based on tags</li>
<li>Provides JSON(P) feeds of tag results</li>
</ul>

FreshTags

Integrates FreshTags functionality into WordPress...

A big cloud of all your blog’s tags is cool and all, but I thought it might be 
fun to try to integrate tags into the whole navigation scheme. Altocumulus will place a cloud of related tags at the top of your Category and Tag pages.
If people are interested and I have the time I’ll try adding more 
functionality. Thanks for trying it out.
You can see a sample <a href="http://www.unsoughtinput.com/index.php/tag/the-internet/" rel="nofollow ugc">on the internet</a>.

Altocumulus

Altocumulus places clouds of related tags on your Archive pages.

FreshTags vs Altocumulus