This plugin will take all tags within your blog and compiles a visually related list for sorting through posts quickly with single-click-filtering.
With the Related Tag Filter (RTF), you get list of the 10 (this is configurable in the admin widget section) most popular tags on your site to date. By simply clicking the related tag you want to sort on, you refine the list to only those that are, you guessed it, RELATED! There is a Show-All-Tags which will show a modal window of every tag used in the blog (NOTE: this also resets the search criteria if you have previous conditions already filtering from the standard selection menu). As well, there is a Reset-Tags link that removes any filtering you may have done, greater than 3. The X on the selected tags are for removing it from the filter. And just in case you have experience with this sort of thing, you will be pleased to know that it IS compatible with pretty PERMALINKS.