I use
DoIKnowYou and I love it. I can mark all my black and white list people, and it auto-shares in the guild for other people with the add-on too. There's a visual colour marker by a person's name if they talk in trade or something, and it notifies you with a warning and your note about the person if they whisper you, if you join a group with them, that kind of thing. And it shows in the tooltip when you mouse over them. It shares across all your characters, too.