Discover which keywords your site visitors are googling to reach your site. Build automatically a tag cloud based on realtime usage data, not on the tags that you THINK are appropriate. Fully customize the tag cloud links and keywords. Ban inapproriate keywords with one click. INSTRUCTIONS: Just activate the plugin, place one of the three available Keyword widgets in your sidebar, and wait some visitors come from a search engine to see the first keywords.
A few notes
<ul>
<li>Tag Cloud is updated each time a page is being visited from somebody who found it on a search engine
<ul>
<li>Same IP can’t fool too much – IPs are logged and considered by the algorythm</li>
<li>Configurable pagerank shaping: follow/nofollow links</li>
<li>A good keyword tag cloud will be the result of a semi-automatic refining process</li>
<li>The keywords you select stay forever and pass PR</li>
<li>less important ones go away eventually!</li>
</ul>
</li>
</ul>

Keywords Cloud for WordPress

A WordPress widget able to store and display in a tag cloud the keywords that your site visitors are using to reach your site's pages.

Waterloo Plugins

Tag Cloud Widget adds a simple tag cloud widget that you can use anywhere on your blog. This plugin looks at all your tags and displays them in a widget. The more times a tag is used, the larger the tag is.
Each tag is a link to the tag page (e.g. http://your-site.com/tag/your-tag). This will help with SEO.
Currently, there aren’t any options to customize the tag cloud. It should work well out of the box. In the future, there may be options to customize the widget.

Good

A tag cloud widget with links to your tag pages

Keywords Cloud for WordPress vs Tag Cloud Widget