by digitalemphasis on WordPress.org
Looks for already existing tags within your posts.
Already Existing Tags - administration panel
This plugin detects your ‘already existing tags’ into your post each time you create or edit/save one. The found tags will be automatically assigned.
Add tags in head of page as meta's keywords
This widget add a tag cloud 3d to your sidebar.
Another wordpress tag cloud plugin based on jQCloud, which is creative, beauty and colorful.