Gmail and Calendar has a great built in task manager that is simplistic yet powerful in its abilities. With this tool, you can link emails to tasks, set due dates, organize your tasks into lists and much more. Check out this CNET article on how to get the most out of using Google Tasks.
Oh, by the way, you can also access a widescreen view of your tasks by going to this link! Helps to sort them out a little bit better.