First of all, Joel has a great article called Painless Software Schedules. He explain what should you do or don't.
Have your ever look Toodledo ?
Organize Your Tasks. Use folders, tags, contexts, subtasks and more to
organize, search and sort through your tasks.
Improve Your Productivity. Toodledo's hotlist, customizable alarms,
and sortable online to-do list will help you remember to complete
Go Anywhere. Get Toodledo on your mobile phone, in your email, on your
calendar, integrated directly into your web browser, and more.
Collaborate. Easily work with other people on shared projects with
Toodledo's collaboration tools.
Customize. Select fields you want to use and define how you want to
view your tasks. Toodledo is incredibly flexible and customizable.
Import Your Existing Tasks. If you already use a task manager, import
tasks from many sources.
And It's free. I know it isn't the best tool for this but I found it very useful. And It's good for me.