Anyone who has spent any time exploring the dozens and dozens of different systems out there to get and stay organized will have come across the use of index cards in several places. The cards are used in all sorts of ways depending upon the system — making lists, capturing ideas, sorting priorities or keeping your thoughts in a visually and adaptable manner. I am personally a sometimes-user of index cards. I believe in them (their easy to get, easy to use and easy to carry), but I haven´t yet got in the habit of using them enough to become addicted to them.
Of all the uses of index cards I have seen, though, none of them are nearly as good as a site called Indexed. Each day the creative genius behind the site uses an illustration on a simple index card to make a complex issue easy to grasp. Don´t worry, though — it´s not a heavy site. It´s usually very funny, and it is more often than not thought provoking and intriguing as well. It may actually be a detriment to productivity because you will spend time looking through the site instead of working, but I visit it every day and it makes me happier and therefore more productive. Check it out. You may never look at index cards the same way again.