For implementing GTD you might try out this new web-based application:

http://www.gtdagenda.com

You can use it to manage your goals, projects and tasks, set next actions and contexts, use
checklists, schedules and a calendar.
A mobile version is available too.

As with the last update, now Gtdagenda has due date for tasks (you'll see in the calendar on the right if you have tasks due today), task notes, and Email & Print support.

Hope you like it.