Tags from a user experience standpoint are a revolutionary invention. With the social media craze has come the idea of tagging posts and photographs. The social news script Pligg CMS does a very good job at including tags for submitted news stories. Users can organize their bookmarks or submitted links based on topic, items, or people.
But even more than the system of tagging is designing the interface. You have to consider how a tag system would look for any given website or application. In the showcase below I have collected dozens of different graphics related to tagged content. Some of these designs are better than others, but all of them portray a very popular current trend in digital media.