Rapportive has raplets. (http://raplets.com)

We also allow you to quickly set reminders on individuals with whom you'd like to stay in touch.

That's actually pretty huge all by itself - I got a YC interview from making a demo of that feature alone at a startup weekend last year.

http://gosnoozemail.com

It had a few other features too and I ended up having to defer the interview until I could find a cofounder.