Resending the e-mails seems to me to be the easiest way to remind people. When I send an e-mail that is going to require the other person to do someting, I bcc myself. When that e-mail appears in my in-box, I drag it to the Outlook task icon and assign a category of @Waiting For. During the weekly review, if I decide I need to send a reminder, I drag the task to the e-mail icon, address it, edit the subject line, and send. All of this assumes that you WANT to remind people.
It may be that you are dealing with people who don't think they need a system because somebody will bail them out. They need to have a few things blow up in their faces so that they will realize they need a system and will be receptive to what you have to offer.