jonkemp

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.
Changelog
*1.1.2 
**Bug fixes. 
*1.1.1 
**Bug fix where if user did not set nofollow pages, pages links would not display. 
*1.1 
**Added support for nofollowing login and registration links. Also, optimized some of the code. 
* 1.0 
**Added support for nofollowing individual pages in <code>wp_list_pages</code> function. 
* 0.5

Ultimate Noindex Nofollow Tool

Improves your blog's search engine optimization by "noindexing" pages you choose.

Fabio Santos

This plugin adds a simple checkbox in the insert/edit link popup for including nofollow attribute.

Rel Nofollow Checkbox

Adds a checkbox in the insert/edit link popup for including rel="nofollow".

Ultimate Noindex Nofollow Tool vs Rel Nofollow Checkbox