jonkemp

Adds the “nofollow” rel attribute to category links.

Nofollow Categories

Adds the "nofollow" rel attribute to category links.

texttheater

Improves your blog’s search engine optimization by “noindexing” pages you choose.
Add the <code>noindex</code> robots meta tag to archives, categories, search pages, tags, author pages, login, admin pages or any other page you choose.
Add the <code>rel="nofollow"</code> attribute to individual pages listed by the <code>wp_list_pages</code> function or the Pages widget. Also, add the <code>rel="nofollow"</code> attribute to archive links, category links, registration and login links.
Written by Jon Kemp, currently maintained by Kilian Evang.
<h3>Usage</h3>
After installation, the settings page for this plugin can be found in your WordPress administration interface under Settings → Ultimate noindex.

Ultimate Noindex Nofollow Tool II

Improves your blog's search engine optimization by "noindexing" pages you choose. Now also for page-based (as opposed to date-based) archives.

Nofollow Categories vs Ultimate Noindex Nofollow Tool II