slaptijack

Suggest Tags creates a list of tag suggestions based on the content of the post you are editing. Since the Yahoo! Term Extraction API is going to be shutdown at the end of August 2009, this plugin uses the term extraction API from tagthe.net.

Suggest Tags

Suggest Tags uses the tagthe.net tagging web service to generate a list of tag suggestions.

Birchdunford

Tags, tagging, and post tags made easy. Stop thinking about what tags you should add, forgetting to add certain tags, and typing in tags by hand. Let Tagbag do the work for you. Just look at the list of suggestions, click the ones you want, and move on. More on Tagbag: 
<a href="http://www.explodybits.com/2012/04/tagbag-wordpress-plugin/" title="explodybits (xb)" rel="nofollow ugc">explodybits (xb)</a>

Tagbag

Tagbag, takes the thought out of selecting tags for your post

Suggest Tags vs Tagbag