Changing the default admin username in WordPress is a no brainer. It is a basic security measure you need to take to make the job of hackers a bit more difficult. Many folks go about doing this by removing the admin account and adding a new username with admin rights. The Username plugin can make the job even easier.
The Username plugin lets you change the admin username without affecting other usernames. All the admins you have can change their own usernames. The plugin does show you when the username you want is already taken. Simple but does the job. Now there are no excuses for not changing your admin username.