Stefan M.

This plugin will set all Trackbacks and Pingbacks automatically to DoFollow Links.
The user comments will get after <code>X</code> comments from a unique mailaddress automatically DoFollow status. All other comments have NoFollow, except the Admin enable manually the DoFollow Status. The status which is set manual (if DoFollow or NoFollow) will overrides the automatical process. So, you have the control if someone gets sooner the DoFollow status, or never maybe. Of corse, the automatism can be disabled to do the hole work manually.
You get an support automatism, that you don’t need to check daily, but have the full control power.
Additonal this plugin validated all DoFollow URLs and will notice if there are broken links. Broken Links are very bad the Rank in the Search Engines (SEO).
Home Page of the Plugin: <a href="http://blog.murawski.ch/2010/09/wordpress-manual-dofollow-plugin/" title="IT Blögg - WordPress Manual DoFollow Plugin" rel="nofollow ugc">IT Blögg – WordPress Manual DoFollow Plugin</a>
If you have a wish for new functions, please contact me.

SMu Manual DoFollow

SMu DoFollow has many DoFollow Options (Manual or Automatism) and included URL Validator (Manual, WP-Cron or Cronjob).

Nikolay N.

Simple plugin that will improve your onsite SEO a bit and make all links from the comment section dofollow, if they point to your own domain. Other links that point to external websites will remain nofollow. WP DoFollow Comment Links don’t have any configorations – simply activate it and that’s all.
It also works with WordPress installations that reside in a subfolder. For example, WordPress installed in example.com/blog, separate from the main website example.com.
If you have any questions or suggestion, hit me up… nnikolaev [at] sematigo.co.uk

WP DoFollow Comment Links

The plugin automatically makes all the comment links to your own domain dofollow, while all external links remain nofollow.

SMu Manual DoFollow vs WP DoFollow Comment Links