The Advanced Tag Entry WordPress plugin extends the built-in tag functionality of WordPress 2.3 and higher, giving you new ways to manage the tags on your post. It adds a new section to the post editing screen, that lets you:

• Add a tag to your post from a drop-down list of existing tags you have already defined on other posts (so you can make sure you are consistent).
• Remove a tag from your post from a drop-down list of the tags you have already added to your post.
• Create a new tag, by defining the tag name and tag slug.
• Edit existing tag names and/or tag slugs.
• Delete tags that are not actually being used, from the WordPress database.

Plugin Page

Advanced Tag Entry, Plugin WordPress Plugin, WordPress 2.3, Tag, WordPress Tag, Technorati Tag