The 4" x 6" white ruled index cards in the 500 pack purchased from my local Staples store are exactly what I need for keeping track of a number of activities and aid in good organizational arrangement. The cards I obtain from Staples are good quality are lightweight and are ruled in a very usable manner. Specifically I keep track of what TV programs are recorded on my DVR and I then can check off the titles when viewed. I also arrange needed thoughts when composing any written papers and then place them in proper order. Staples cards are all uniform size and allow for easy storage. The price is right and there is no need to purchase expensive branded products.
This multi-pack is a great deal. My wife uses them for many purposes including business shopping and organizing tasks here at home. She finds them quite useful. I sometimes use them if I am doing any object oriented programming using the Wirfs-Brock method for initial design. Having the information on this size of card makes organizing the objects needed for the program so much easier than anything I have found on the computer. I group them and then see which have common elements and which are actually subsets of other objects. It makes programming much easier. In fact I would do this before any agile programming because I know what I need to code before I do it.
My son is a high school teacher and also coaches the indoor track team. He uses 4x6 index cards to record and submit the names of his athletes for their individual events. As he has over 70 students on the team and as each one competes in at least two events he goes through a lot of index cards. Needless to say the Staples brand index cards in the 500 pack are not only convenient but are a good buy. I purchase them for him periodically when buying my own office supplies - this allows me to get credit on my Staples rewards!
I purchased these for my daughter for school - she loves them because the lines are wide enough to write legibly yet small enough that she can fit the items she needs for an open note-card test.