To get a grip on a busy inbox, keep on top of important emails by giving them Superstars.
- Generic Star
- Waiting for response
And with multiple inboxes in Gmail, you can have one of those inboxes just for showing messages with one of those stars. So 5 entries from my TODO list sits above my inbox. That way I'm always atleast concerned with keeping on track.
There are other stars, but I haven't felt that they make more any more productive. Maybe as I have even more plates to balance.