BuddyPress Activity Filter is a useful plugin that allows you to customise the the way the BuddyPress activity feed works. It allows site admins to limit which filters are available on the activity page, limit which activity filters are available on the main site-wide activity page and customise the activity updates for each post type.
BuddyPress Registration Groups is a plugin that adds a list of groups to the registration form so that new members can be introduced and join your groups. It means they don’t need to go looking for them to be instantly tied in to their preferred groups. Adding this kind or form to your registration can help you to build a profile for each new member.
Avoid Duplicate Titles is a plugin for WordPress by BuddyUser.com. Whilst it’s not specifically a BuddyPress plugin it is very useful for multi-user situations where there is a high chance of users creating posts with duplicate titles.