Konstantin Obenland

This plugin replaces the author slug with a sanitized version of the user’s display name.
This plugin will not prevent hackers from finding out your login name but the login name won’t be visible 
in the author archive’s URL, which works towards your friendly URLs with using your display name.
DO NOT use this on a site with more than 1000 registered users, as updating all of their nicenames at once might break your site.

WP Author Slug

Easy way to add some obscurity to login guessing.

But please update as it's over 2 years now.

Excellent

This plugin would probably work OK if you have a small number of users (e.g. if your site doesn't allow public login). But if you have a large number of users (e.g. if you are running ecommerce or allow users to register for other reasons), this plugin will probably take down your site.

The reason is that there are hooks that run when you activate or delete the plugin. It runs database fetch and update queries on every user in your database, all in-line on the request (rather than background via a cron). So if you have a thousand or more users it attempts to do a thousand or more database writes when you click Activate or Delete from the plugins list. This will likely grind your website to a halt. 

It would be better/useable if you could either choose to only apply these scripts to specific user types (e.g. Author) or if you could run the update in batches in the background.

Don't use if you have a large user database

Add a layer of security and prevent your login name from being shown in the author archive's URL.

yonisink

yContributors creates a one-step author or contributors archive page that enables you to show any number of recent posts by each author, along with profile information pulled from each user’s wordpress user profile. This plugin shows all your members, either in table or descending form, with a jQuery searchable autocomplete-style (type and find) way to get to members. Options include excluding certain members, showing latest posts and author statistics. Also, works with User Photos Plugin (unrelated to this) to display profile photos.
For more information visit http://social-ink.net or http://www.social-ink.net/blog/ycontributors-wordpress-plugin-for-author-archives-and-contributor-index-with-photos-and-excerpts
Please note, as with every plugin or theme modification, you should do a backup of your files beforehand. Although we’ve tested this across many installs, we are not responsible for anything it does to your system and do not guarantee support.

yContributors

yContributors easily creates pretty, jQuery-searchable contributor/author indices and author and contributor archives.

WP Author Slug vs yContributors