Members Import is a WordPress plugin by manishkrag that allows you to batch import of users/members taken from an uploaded CSV file.
It will add users/members with basic information, including firstname, lastname, username, password and email address. Each user who is added will be a ‘subscriber’ if value not provided in csv file, and be able to login to your site.
You can also choose to send a notification to the new users and to display password nag on user login.
Download: http://wordpress.org/extend/plugins/members-import/