Comment Guard Power Pack - Comment Guard Pro Power Pack contains 7 very useful pluglets to augment Comment Guard Pro (which is bundled with 15 pluglets).
Note: Comment Guard Pro plugin protects your blog from all types of comment spams.
Referrer Bouncer - A Plugin to bounce back referrer spam attempts, requires no upfront configuration, no mod-rewrite. It is like the strong silent bouncer at your favorite club. Tested on all versions of WordPress.
Feed Copyrighter - Feed Copyrighter adds a copyright message to your feed items. No customization is necessary. This acts as a strong deterrent to feed-stealers who unscrupulously and blatantly displays your full feed contents (often with their own advertisements) in their site(s) without your permission which can not only hurt you in terms of revenue but also incur duplicate-content penalty from search engines.
No-NoFollow - Give credit to your commenters for their hard work