Have you tried Remember the Milk yet? It is a simple, open-source tool that helps you electronically record and track To Do lists . . . I started using it after a recommendation from a colleague who really likes to combine it with Google Aps. If you have Google Aps (another free resource), you can connect your Remember the Milk to both your Google Aps email account and/or your Google Calendar.
I like the fact that I can have it right there on my screen when I am working on other common tasks like my calendar or using my email . . . and I can schedule my tasks as well. I find this really useful for things that don’t have a real deadline, but I want to remind myself to deal with. You can easily postpone the task as well. Or I like to leave a task as Overdue so I remember that I am backing up on some things and really need to create some time to get these non-urgent tasks done.