Have a profile page for each user with an avatar and banner, what they could optionally fill out with some information about themselves.

Also, have a place or a link on every profile page where you could see the edits, comments, and contributions of the user, and a message wall for every profile page where you could publically message the users and discuss stuff, and maybe have a private messaging system as well. An automatic customizable greeting message on the message wall of newly registered users would be nice as well.

Much like on social media sites, and on wiki farms like Wikia and Gamepedia, and in MediaWiki's SocialProfile extension.