Nick Momrik

When writing comments, a lot of people type in google.com, yahoo.com, hotmail.com, and various other web sites which don’t belong to them. This plugin strips out the comment author URL whenever it contains anything from a set of words that you specify in the Options screen. The URL will never make it to the database.

Comment Author URL Stripper

Removes the comment author URL if it contains any of the specified words.

Jared Harbour

Ever want to change the url used to display your posts? This plugin 
allows a blog administrator to change a users url slug from their edit profile page.
The plugin allows for the creation of new author slugs, but also saves old slugs a user has used in the past.

Plugin Name:       Modify Author URL

Allows administrators to modify a users author url from their profile page.

Comment Author URL Stripper vs Plugin Name: Modify Author URL