BuddyPress.org

Of the sites that I can remember from the top of my head:

http://www.studiopress.com/announcements/genesis-connect-1-0-plugin-for-buddypress-available.htm
http://buddydress.com/themes/
http://bp-tricks.com/purchase-bp-slick/
http://www.buddyboss.com/themes/

And, of couse, those listed in the theme website; https://buddypress.org/extend/themes/