Remember The Milk is my To-Do manager of choice. I have tried a few others, and found that the various places RTM finds placement is what pushes it over the edge. I see RTM tasks on it’s website, my gMail, and my iPhone. Sure, the Pro account (required for iPhone app) costs ya about $25/yr, but I think it’s worth it. It supports uploading tasks via eMail, and you can hook it up to a Jott account, and get your tasks into your account via voice. The iPhone app supports GPS-based location monitoring. Tasks can be sorted into user-created lists – you also have the ability to create smart lists based on search criteria. RTM has iCal feeds for both events and tasks.