Ignore me, too! (automatic)
What I hate most about modern email times is that more and more people believe that emails can be simply ignored. While this is partly understandable and probably due to the rising wave of spam that is sent by machines anyway, I find it incredibly annoying when you really have a request or problem and are longing for an answer.
1. An "I definitely want an answer" setting. Your email program will monitor if you received a reply to a particular message, and if you didn't, it'll send out a second mail insisting that you are still waiting for a reply. Such a second mail usually works very well if sent manually, but I find it increasingly difficult to keep track of all of the mail I have sent that has remained unanswered.
2. An "ignore me, too" setting. - Sometimes, the "I definitely want an answer" setting will fail. Some people are simply impolite, they won't reply, or it'll take them forever to answer. Then, all of a sudden, they need something themselves, and then it has do be done really quickly, of course. My suggestion is an "ignore me, too!" setting in the email program. Once activated, it'll keep track on how long it took someone else until they finally got their reply out, and it'll delay your own message for the same time span.
Reward: A free copy of the software.