The ultimate task manager/To Do program out there is REXwireless' To Do Matrix.
. Nothing else comes close to the power of this app.
The cons of it are:
1. Price. $59.95 on a stand-alone basis, less if you buy it with other apps REXwireless offers.
2. Interface looks like something from the days of the BlackBerry 7200-series. This can also be a plus though. Simple to use, easy to navigate, easy to find things.
Whether or not you buy it you should download the free white paper on getting things done: Best Practices