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

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.

Tag Cloud Widget vs Custom Tag Cloud