One of the main tenants of the GTD methodology is the idea of ubiquitous capture. That is, a way to always get that stuff you have floating around your noggin out of it and into a trusted system that will allow you to evaluate it later. For many, having a pen to write stuff down with at constant disposal is the easiest, quickest and most cost effective solution for this. Problem is, most pens are better designed for the shirt pocket than, say, any other pocket that you more regularly have available in this increasingly casual society.
That being said, here is a rundown of some stealthy pens that can fit in all manner of other places so that you are never without a way to jot down that next great idea (or just an addition to your honey-do list):
Lamy Pico – This is the one I own. The Pico is a really stylish and slick little pen that is the size of a really small cigar when closed and extends to a full size pen when open. I actually keep it in the bottom of my wallet with some half-size index cards thrown in to complete the kit. Although this combo is not my main capture device, this helps ensure that I am never without one.
The Inka Pen – Really small when closed and has a loop that attaches to your keychain. Once detached, it converts to a full size pen and even has a PDA stylus. This is one I would have gotten if I had not seen the Pico first.
Levenger Silvertini Wallet Pen – This small, elegant, sterling silver pen is designed to attach onto a wallet, checkbook or other small personal accessory. It is only three inches in length so it can fit almost anywhere and has a strong clip so it wont get lost. It does not expand to a full size pen so you will not be writing a novel with it but that is not the point.
Bookmark Pens (via David Seah) – I have yet to find these but they sure do look interesting. They are sold as flat pens that are designed to attach between the pages of a book. They kind of look like they would make a book the size of a Moleskine bulge a bit but it might . David has a good write-up if you follow the link.
FoldzFlat Pen – This is a pen that folds into a flat unit the size of a business card for easy carrying in the card slot of a wallet. Looks kind of goofy to me but there are no points for style in this list – only functionality.
Pilot G2 Mini – The Pilot G2 was my pen of choice for a long while and is a fantastic gel roller with unbelievable smoothness. The mini version is just a good but in a package small enough to carry in a front pocket with little notice of it being there. A good and cost effective solution.
Zebra F-301 Compact – This is another “convertible” pen. Only 4 inches when closed it converts to a regular size pen once opened. Another cost effective solution.
(Late stage addition)
Fisher Space Pen – How could I have forgotten the venerable Space Pen? This lovely little feat of space age design is certainly small enough to carry in the pocket of your choice and can write on almost anything. This is the pen of choice for many a GTDer. I have been properly scolded for this original omission in the comments.