Make Active "Commentors" Famous
Here’s yet another way to recruit talented guest contributors for your site: Let the talent come to you.
Do this by watching your comments section. Whenever a commenter makes an astute point about an article, run a background check.
If they provide a link to their site, do some reconnaissance to determine if they may be a good candidate to write for your site.
You already know that they are actively commenting and networking on your site, so chances are they would be willing to write a post or two for you. They'll also likely continue their commenting, creating a great conversation and boosting content recognition as well.
Resources:
http://www.problogger.net/archives/2007/02/28/how-to-find-a-guest-blogger-for-your-blog/
jimmybt