I’ve just released Ultimate Tag Warrior 1.1 into the wild! From here on (and indeed since last week), the latest version of Ultimate Tag Warrior is going to live here: http://dev.wp-plugins.org/browser/ultimate-tag-warrior/trunk/. I’ll keep on announcing new versions of it here, though.
Version 1.1 adds ultimate_show_related_tags(), which will display the tags related to the current tag set. If you are viewing /tag/monkey, it will list all of the tags of the posts that match monkey (except for monkey itself.) If you are viewing /tag/monkey+banana it will list all of the tags of the posts that match both monkey and banana (excluding the monkey and banana tags). Clicking the + beside a tag will add it to the tag set.
made me write this suggested this feature.