I found a plug-in which make links by commenter’s Dofollow instead of Nofollow which is the default link type for WordPress. All you need is to upload the dofollow plugin from SemioLogic.com and activate it in WordPress Plugin Control Panel.
By making your links DoFollow instead of NoFollow, your commenters will also get more link juice. Some of your visitors will also be more likely to comment since they will get more dofollow back links to their website which increases their Search rankings in Google and other search engines. DoFollow is great for Search Engine Optimization.
Update: I decided to make this blog NoFollow again since I don’t have the time to moderate spammy comments and comments which are poor quality like people who post “thx” which I tend to be getting after I change this blog to DoFollow.
Download WP Dofollow plugin at http://www.semiologic.com/software/dofollow/