iDo is a to-do list manager that uses the Getting Things Done (GTD) approach. Using iDo you can easily organize your to-do tasks into projects and contexts. The best part, there's nothing to install, all you need is a web browser. If you have an iPhone, even better. Sign-up now for your free trial, or Login if you already have an account.
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 and iCal are available too.