BuddyPress: Username Rules on the Sign-Up Form
Requires BuddyPress usernames to be at least a few characters long and not just numbers, giving members a clear error message on the sign-up form.
Snippet Library
Users snippets for WordPress
Snippets for user accounts, roles and profiles: extra profile fields, new columns in the users list, last-login tracking and tighter control of what each role can do. Handy for membership sites, client sites and teams with many authors.