1. All in One SEO Pack
Automatically optimizes your Wordpress blog for Search Engines (Search Engine Optimization).
2. Simple Tags
Simple Tags is the successor of Simple Tagging Plugin and is THE perfect tool to manage perfectly your WP 2.3 or 2.5 tags (Related Posts, Related Tags, Auto link tags, Tag suggestion, autocompletion, click tags, Mass Edit Tags, etc.)
3. Simple Trackback Validation
Simple Trackback Validation Plugin for WordPress 2.x performs simple but very effective tests on all incoming trackbacks in order to stop trackback spam.
4. Wp autoblog