Ultimate Tag Warrior is really the ultimate wordpress plugin for tag management, but unfortunately it is no longer developed and not compatible with latest wordpress versions. My online buddy Keith Dsouza just released a tag management plugin called Better Tags Manager. As the name suggests it is better than some of the tag management plugins.
What it does?
Better Tags Manager (BTM) allows you to edit tags from the manage post section without having to visit the post itself.
In addition to that it will allow you to filter out posts which do not have tags and edit or bulk edit them. If you do not want to edit tags individually you can filter out and edit bulk posts at once by choosing the bulk edit option.
Another cool feature of the plugin is that it allows you to add tags to multiple posts with out having to edit posts.