I'm new to GTD, so I apologize for the lateness of this post to the topic.
As I was reading the book, I realized the GTD philosophy is similar to the European planner system I used a few years ago. It is called Time/Design and can be found at www.timedesign.com. The system and forms are somewhat expensive since they come from an European source. The thing that struck me was how the pre-printed forms seem to fit right in with David's philosophy and process.
If you are looking for a paper planning system that is compatible with GTD, you should checkout Time/Design.
They also offer a compact version for people who use a PDA.