WP Cumulus is a plugin that collect your tags and display it in a very nice rotating 3D Flash sphere, it allow you to predefine the amount of tags you want to display. Other than tags, you can also display your blog categories, or even both!! Clicking on the tag or category will take you to the appropriate page.
A lot of customization you can do with WP Cumulus, like the width, font color, background color etc, so you don’t have to worry that WP Cumulus will break your theme.
You can see the WP Cumulus in action at my sidebar.