To disable nofollow in your WordPress comments, use one of the following plugins:
Nofollow Case by Case – Allows you to turn ON the nofollow attribute for SELECTED pingbacks, trackbacks, and comment links. This works well if you moderate the comments on your site.
DeLink Comment Author – by Alex King. This plugin gives you the ability to remove the link a commenter left as their URL without removing the entire comment. A link to do this is added to your new comment e-mail notifications and to the comments list in your admin area.Â Alex has a nice list of plugins that he’s developed.
Ultimate List of Dofollow & Nofollow Plugins – This is a well-maintained list of plugins to add nofollow and remove nofollow from various elements of WordPress. The list also covers other blogging platforms such as Blogger, Moveable Type, Typepad and Drupal.
Comprehensive Reference for WordPress NoNofollow/Dofollow Plugins – A concise, current, and comprehensive reference for WordPress no-nofollow and dofollow plugins. Currently featuring 12 dofollow/no-nofollow plugins, this ultimate guide will help you choose the best plugin for your blog.
NoFollow Free – Includes the option to use dofollow only when the author has posted a certain number of comments, and to put back the nofollow when some blacklisted words are matched.
Also, be sure to check out CommentLuv – This plugin will visit the site of the comment author, while they type their comment, and retrieve a selection of their last blog posts, tweets or digg submissions which they can choose from to include at the bottom of their comment when they click submit.
The WordPres Codex – has also provided some resources to help you find do-follow plugins.