WordPress.org

Easy Tagger plugin lets subscribers to your blog add tags, search posts by them, display search results in nice image grid (for that one has to previusly set Featured Image for each post to display), it also shows some basic statistics like most popular tags, most active users, recent tags, etc.

Notice

Plugin creates tables wp_users_blacklist and wp_users_terms_posts for it own purposes check if those don`t already exist in your wordpress installation (some other plugin).