Yesterday I installed a plugin for [tag]Wordpress[/tag] called The Ultimate Tag Warrior. Using this plugin I can tag posts and categories, link the tags to various services
such as [tag]Technorati[/tag] and [tag]Wikipedia[/tag] (among others) and I am able to make tag clouds,
showing you the most used tags on my site.
At the bottom of every post, you can see the tags I have used. You can either click the tag
and see all posts with the same tag, or you can click on the >> on the right side of the tag, then you will get access to posts using the same tag at other sites. Just click on the icons.