Marcin Pietrzak

Add a full tag list to your site.
<h4>Translators</h4>
<ul>
<li>Belorussian (be_BY) – <a href="http://pc.de/" rel="nofollow ugc">Marcis G.</a></li>
<li>Polish (pl_PL) – <a href="http://iworks.pl/" rel="nofollow ugc">Marcin Pietrzak</a></li>
</ul>
If you have created your own language pack, or have an update of an existing one, you can send <a href="https://codex.wordpress.org/Translating_WordPress" rel="nofollow ugc">gettext PO and MO files</a> to me so that I can bundle it into Tag list. You can <a href="https://plugins.svn.wordpress.org/tag-list/trunk/lang/tag-list.pot" rel="nofollow ugc">download the latest POT file from here</a>.

Tag list

jfoucher

This plugin uses the yahoo.com API to find the most relevant keywords from the content of your post, and then adds them as tags.
The tagging is fully automatic, so if you’re using a plugin like feedwordpress to display RSS feeds on your blog as posts, everything will get done as the feed posts are published. No user intervention necessary!

Auto-tags

Automatically add relevant tags to new posts.

Tag list vs Auto-tags