NextActionCards.com
I'm thinking of trying these because they are small - I can't print business card size on my printer unless I buy that paper that has business cards on them that you then cut out. I have played with them, but they are expensive (more than 2X the cost of what this guy is selling - probably more if I figure in ink), time consuming to print and even more time consuming to detach from the paper. I could be wrong, but I think D.I.Y. contemplates index sized cards, which for me have been to bulky to carry around. $10 doesn't seem like a bad deal - it would have to take me at least a half hour to print up 250 myself.
In fact, I have used the back of my own business cards as a capture tool, but this guy's design looks to allow for quicker categorization and organization. Of course, his design is not perfect, but I think we would all do our own separate designs if we were doing that, based on how we personally use GTD. If I try them, I'll let you know how they worked for me.
Steve