There’s another Thing for wordpress!
Tag Managing Thing is pretty sweet. It adds a new window to the WordPress admin system which allows you to modify tags (and categories! (and things in any other post-based taxonomies you acquire through other plugins… Oooh! Exciting)).
Tags Terms can have their name and slug changed; and can be deleted. Two pedestrian, but none the less useful bits of functionality.
It’s also possible to split an existing term into a number of new terms; and you can merge existing terms into a single term. Two much more interesting things to be able to do.
Ooh, and this is my favourite. You can change the taxonomy that a term belongs to. Which is to say, you can turn a tag into a category or a category into a tag. (And if you have additional taxonomies for post objects, you can also move terms into and out of those taxonomies as well.)
I think it’s pretty neat.