srcoley

This wigetized plugin shows the gravatar and info of the most recently active authors of your blog. The author with the most recent post will be displayed first, the author with the second latest will be displayed second, and so on.
Awesome Authors allows you to select ‘Sticky Authors.’ These authors will be displayed at the front of the list no matter how long ago their latest post was published. Conversely, you can select authors to be ‘Excluded Authors.’ These authors will never be displayed in the list no matter how many posts they have or how recently their last post was published. You can also set a minimum post requirement. If you set this to, let’s say 10, then only authors with 10 or more published posts will be displayed on the Author Bar. Some of the other options include gravatar display size, and how many authors overall to display.

Awesome Authors

This wigetized plugin shows the gravatar and info of the most recently active authors of your blog.

freshdevelop

This plugin is useful to streamline user addition: by placing a small contact form straight in the homepage, users have a direct tool to ask becoming a website user. By the other side, admins can accept everyone with a single click, or inspect incoming requests one-by-one within the detailed table.
Warning: wrong use of this plugin can be extremely harmful. Please read everything carefully before adding unintentionally unwanted candidates and/or spammers.

Can I write for you?

Allows users to put themselves to become blog authors. Widget visualization and email notifications added.

Awesome Authors vs Can I write for you?