bjplink

Export Comment Authors lets you extract the Names, Email Addresses and more of your Comment Authors into a CSV file. This plugin is a great way to jump start a newsletter by importing the resulting CSV file into any of the popular newsletter services like MailChimp, AWeber or Campaign Monitor. It can also be used to extract information on a per post basis for things like contests.

Export Comment Authors

Export Comment Authors lets you extract the Names, Email Addresses and more of your Comment Authors into a CSV file.

mattdu

This plugin uses the custom taxonomy features of WordPress to create “bylines” — essentially, tags representing authors who contributed to a post. The differentiating feature of this plugin is that it should not require any modifications to your theme files (assuming it is already displaying the post author).
This plugin would be useful for publishing situations where the majority of your content is from contributors who you don’t necessarily want to have access to your back-end. It still conveys the appearance that the authors are members of the site (it provides a built-in archive page for each Byline). If your theme displays tag descriptions, you could use the Byline description field to identify guests vs. “staff” writers or provide other author information.
You can see an example of this plugin at work at http://thedailycougar.com

Byline

The Byline plugin is simple and suitable for multi-author WordPress sites.

Best For Multi Author

Solves the co/multi-author problem without modifying the theme. Uses a custom taxonomy, "Byline," that replaces the Display Author.

Export Comment Authors vs Byline