Permit a user to create new accounts
Use the Role Delegation module.


  This module allows site administrators to grant some roles the
  authority to assign selected roles to users, without them needing the
  administer permissions permission.
  
  For each role, Role Delegation provides a new assign ROLE role
  permission to allow the assignment of that role.
  
  The module also adds an assign all roles permission. Enabling this
  permission for a role is a convenient way to allow the assignment of
  any other role without having to check all the assign ROLE role
  permissions in the Permissions page.
  
  If an administrator has the administer users permission, a role
  assignment widget gets displayed in the account creation or editing
  form, and bulk add/remove role operations become available on the user
  administration page. Otherwise, if s/he has at least the access user
  profiles permission, the module adds its own Roles tab to the user
  profile so that roles can be assigned.