Plugins for Better User Experience

I’ll start off saying I absolutely love WordPress, but I’m working on a community magazine and I’d love to integrate some features that would give readers a reason to sign up for memberships. I’ve found it’s really hard to convince people who don’t surf the web all day to sign up, but I figured if there were some cool user-only features (newsletters, or other cool stuff) they might be more inclined. I’m just wondering if anyone has any ideas, or knows of any cool plugins that really expand the reader experience (readers with memberships that is).