A Simple Index Card GTD System

"The system is simple. I use a small stack of colored 3 inch by 5 inch index cards, held together with a small bulldog clip. During the week, the stack resides in my shirt pocket; on the weekends, it moves effortlessly to my jeans or shorts."

Via GTDTimes: http://www.gtdtimes.com/2008/04/28/a-simple-index-card-gtd-system/