maxpagels

Most Popular Tags is a WordPress plugin that allows you to display your blog’s most popular tags or categories as a sidebar widget. The plugin takes advantage of the new Widget API introduced in WordPress 2.8, allowing multiple instances of the same widget, each with it’s own unique configuration. You can specify how many tags/categories/link categories to show, the size of the smallest and largest ones, which unit and format to use as well as advanced ordering options.

Most Popular Tags

Most Popular Tags is a plugin that displays your WordPress site's most popular tags, categories and custom taxonomies as a sidebar widget.

skipstorm

This plugin adds a tag cloud widget where you can select multiple tags at once.
ATTENTION! This is a totally different plugin so if you’re updating from the version 0.6.x you’ll have to configure it again. 
Visit the plugin homepage to download the old version if you want to downgrade.
<h4>Update</h4>
1.0.2 
* Bug fix for utf8 slugs thanks to Alexandros 
* Bug fix + template functions, check comments on plugin homepage
1.0.1 
* Bug fix about random order
1.0 
* Now is a multi instance widget 
* Supports modules 
* Added wp cumulus module (flash file courtesy of weefselkweekje and LukeMorton) 
* Any tag size has it’s own css class allowing a better customization 
* Added several options
0.6.2 
* Removed bug causing some tags not to be displayed, thanks to Felipe from turismocoquimbo.com
0.6.1 
* This version removes the tags that will lead to no articles in the add tag list. 
You might want to install wp-cache to avoid performance issues.
<h4>System requirements</h4>
I’ve only tested this plugin on wordpress 3.0 but it should work down to version 2.8 
This plugin requires php version 5.0 or above
<h3>Developers</h3>
This plugin supports modules, check out the files in modules folder if you want to create your custom cloud style.

Sk Multi Tag

This plugin adds a tag cloud widget where you can select multiple tags at once.

Most Popular Tags vs Sk Multi Tag