Here are a few that I use on a regular basis:
Great for scheduling emails- stay on top of multiple time zones.
Boomerang adds scheduled sending and the easiest, most integrated email reminders to Gmail, helping you reach Inbox Zero.
A simple CRM platform and way to automate emails!
Manage customers directly inside gmail No more back and forth between your inbox and other tools
Great for iPhone! Allows me to check on emails away from my computer.
iPhone App, Great for keeping eye on Google Analytics
So I can send my signature digitally from my phone!
Turn your phone and tablet into scanner for intelligent document management. CamScanner is an intelligent document management solution.
iPhone App: To stay on top of social analytics
I hope these work for you!