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.

The Krotek

Customizable widget and shortcode to display tag cloud anywhere you want. You can use it as standard tag cloud widget, as shortcode in any post or page, or both ways. Tons of options allow you to fine tune cloud layout to your needs.
STANDARD FEATURES
<ul>
<li>Display list of post, category or link category tags.</li>
<li>Define number of tags to be displayed.</li>
<li>Set custom tag separator.</li>
<li>Select tag taxonomy: posts, categories or link categories.</li>
<li>Choose cloud mode: shortcode only, widget only or both.</li>
</ul>
PREMIUM FEATURES
<ul>
<li>Define smallest and largest tag size.</li>
<li>Select size unit: px, pt, em or percent.</li>
<li>Choose layout: standard flat cloud or unordered list.</li>
<li>Order tags by name or count.</li>
<li>Sort tags ascending, descending or randomize.</li>
<li>Define list of tags to exclude from cloud or include only.</li>
</ul>
You can purchase Premium version <a href="https://thekrotek.com/wordpress-extensions/tag-cloud" rel="nofollow ugc">here</a>.

Custom Tag Cloud

...but it at least is a little better than the one that comes with WordPress.

Free version is not very customizable...

Customizable widget and shortcode to display tag cloud anywhere you want.

Keywords Cloud for WordPress vs Custom Tag Cloud