As a maker of lists and a manager of projects, I have tried countless methods for task management and GTD. For me, the best (except for my trusty notebook and pen) is Things, task management software for Mac.
Things is simple software that blends into my workflow. I appreciate that it's not over-engineered and I don't feel forced to conform to someone else's ideas about task management.
Things 1.0 will be released at MacWorld Expo 2009 on January 6 and will carry a price tag of $49 (sign up to the newsletter before the release and get a 20% discount). I won't hesitate to pay for this gem. Oh, and Things is also the most popular paid to-do task manager for iPhone and iPod touch users.