Bulk Import Users by Email Address into WordPress Multisite or BuddyPress
It allows you to import users into your WordPress installation by adding a list of email addresses. Accounts are created for each with usernames based on the email address. If you have BuddyPress installed, the welcome email to your users will include a link to the “Edit Profile” screen to help them get going with their accounts.
This is a handy plugin for educators wanting to import their students or a business directory, family blog, or any situation where you know all your users’ email addresses. Head over to Boone’s site for more specifics on Simple Import Users.