[[!Peoples]]
Use the Peoples extra.
If the user list changes often, you'll want to call it uncached:
[[!Peoples]]
You'll probably want to use the Register snippet (part of the Login extra) to create the users.
As an alternative, you might also want to look at Subscribe, which wraps the Register snippet and provides some extra bells and whistles.
The Notify extra works with Subscribe to send email notifications to users in specific user groups, or who have specific interests.