Generally, I'll make sure to map out complex tasks by breaking them into simple components/milestones, each with a clear deadline. More specifically, I've been

Generally, I'll make sure to map out complex tasks by breaking them into simple components/milestones, each with a clear deadline. More specifically, I've been using Google Calendar for about a year to great effect to keep track of my freelancing, the non-profit I run, and also the side jobs I take (substitute teaching and tutoring). In addition, I use it to keep track of my personal life, including social engagements/obligations and birthdays. The "Tasks" feature and I never really got along, so instead I created different calendars for each domain. Relevant days and times are extremely easy to keep track of (as you might expect). I'll generally store hyperlinks in the "Description" box. I'll also sometimes mark calendar events with an asterisk if there is something in the "Description" box that I need to look at (be it a hyperlink, a "Bring _____" note, or some other actionable item). If there are relevant files, I'll either keep them out on my desktop, or I'll include a hyperlink to the file in Google Docs (under the "Share" dropdown menu). Each morning, my calendar will e-mail me an agenda for the day. Items that I don't complete get moved ahead to the next day (or to a later time that day). If I finish things ahead of schedule, I'll move them back to when I finished them and congratulate myself with a delicious and healthy fruit smoothie. You might find that GCal is suboptimal for your purposes (I don't know how well this meshes with the GTD system, as this has worked so well for me that I've never needed to explore alternatives), and it may be a bit less automated/centralized than what you're looking for. Or perhaps you're leery of feeding information to the Googleplex. But I've found my system to be useful and unobtrusive, so perhaps others might as well.