Wordpress plugin suggestions

Hello everyone. I'm wondering if anyone would suggest some good wordpress plugins they are using on there wordpress sites. My goal is to create decent wordpress sites that are mostly white hat with good articles and other content but I'm testing out different plugins to make the site better. I realize I am being very general here and that's the point because I already have most of the common plugins but I am looking for something that I don't even know exists...yet. Suggestions please.