Rhys Wynne

This plugin quite simply lets you know where the users entered your site when they leave a comment. A lot of people who joined the do-follow movement are listed on sites which are a target for comment spammers. To those who suffer comment spam can now find out the page they come from, and block accordingly.
This plugin uses a cookie to track the commenter, so if the user hits the first page first, they will still be tracked.

InComment

Adds an extra "referral" note to the bottom of comment forms, so you could see where people come from comment. Useful for finding resources  …

Everfluxx

Follow My Links is a very simple plugin that prevents WordPress from automatically adding a “rel=nofollow” attribute to the following two categories of authorial links: 
1. links in the post author‘s comments; 
2. links to the post author‘s URL (usually linked to from the comment author’s username).
<a href="http://www.everfluxx.com/follow-my-links/" rel="nofollow ugc">Read the full documentation at Everfluxx.com!</a>
<h3>Donations</h3>
If you like this plugin, feel free to donate a link to <a href="http://www.everfluxx.com/" title="www.everfluxx.com" rel="nofollow ugc">my blog</a> or <a href="http://tinyurl.com/followmylinks" title="Donate with PayPal" rel="nofollow ugc">buy me a slice of pizza</a>.
<h3>Feedback</h3>
Please do send me your feedback via this <a href="http://www.everfluxx.com/follow-my-links/#respond" rel="nofollow ugc">comment form</a>.

Follow My Links

Do not automatically add the rel=nofollow attribute to links in authorial comments, strip nofollow from links to the post author's web page.

InComment vs Follow My Links