In my quest for getting a GTD system up and going, I came across many different types of GTD system, it ranges from a simple todo list using a manilla folder and post-it notes to an elaborate system using a Moleskine notebook.
I started out using an online system backpackit but it doesn't help much if I am not at my computer. with internet access. It is excellent for the lists of items that can be done form a computer, ie sending an email to Jim for this weekend's BBQ or wirte that article on the blog.
I then moved onto to my Palm T3 PDA. I have had a PDA of one sort or another for almost 8 years now but have only really used it for calendaring and address list. I am starting to using the todo list application on it, and coupled it with something like Outlook, it forms a productive tool. However, I have found that the battery life on those things really suck. I take it away over the holidays period and the battery power was down to almost zero after 10 days. I guess the backup todo list is still the pen and paper until I can recharge the battery when I get back to my desk at work.
I am starting to favour some of the Moleskine hacks around for a GTD systems. They look that they should work OK provided I form a habit of consulting it frequently and make note in it frequently. I think that I like about the Moleskine GTD hacks is the it is accessible all the time and it only relies on having a pen/pencil with it to make a note.
Peter at Getting (Some) Things Done has an interesting spin on the why the Moleskine notebooks. Peter noted that he chose them as then cost a bit more and, psychologically, we will take care of it a bit more because it DOES cost a bit more.
The PigPogPDA is also another popular Moleskine GTD Hack, and it also looks promising.