Google recently added an addon feature for Google Apps called tasks which shows a list of to-do items in your mail view. You can turn it on by going to Settings –> Labs and look for "Tasks." I love this addon because it puts a list of to-do reminders where I spend a good portion of my time – in email. Tasks can even be viewed on your phone.

Even more recently, Google added task integration with Google Calendar, so you can schedule tasks and easily refer to them when in Calendar view as well – here’s more information from Google about it.

Did I mention Google Apps is free for 50 accounts or less? Once you see what it’s capable of, it will revolutionize your workflow.