Ultimate Nofollow is a WordPress plugin by bitacre contains several tools in one to significantly increase your control of the nofollow rel tag on every link on your blog, on both an individual and type basis. It is designed to give you fine-grained control of linking for SEO purposes.
The author says: This plugin is still in beta. While it is stable, not all functions listed are included yet.
The plugin’s main features are:
a nofollow checkbox to the insert link dialogue box,
several nofollow shortcodes (added in v0.1.0),
a nofollow option for individual blogroll links,
add or remove the nofollow tag from all links in comments (added in v0.1.2),
plugin settings page (added in v0.1.1).