bbp Toolkit is a plugin that allows the site admin to make various styling changes to a sites bbPress forum pages plus more besides.
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.
GR Dashboard notes, whilst not being specifically a BuddyPress plugin could be useful for membership sites with a few admin and moderators. This plugin allows you to add notes to the dashboard that will only be seen by members of specific roles. So for example it could be used to send a general note to all admin, and they’d see it as soon as they visited the dashboard.