Gmail labs recently added a new application called, cleverly enough, "Tasks," which brings task management inside of Gmail. If you afre someone who lives in Gmail, then having your tasks there too, makes a lot of sense. If you use Gmail and you understand the principles of David Allen's GTD methodology, then this really
makes a lot of sense. (This is the same reason we built eProductivity
around the Lotus Notes In-box: we wanted to help people to manage their stuff by making it easy for them to process their incoming items at the point of entry.)
I'm not a Gmail user so I can't say anything about the quality of their implementation, but if you use Gmail, it's probably worth checking out.
Gmail labs: Tasks