Digi-Key is a great place to order electronic components. Their online search is great, their prices are reasonable, and (best of all) they use environmentally friendly packaging materials.
A day when a Digi-Key box arrives is a red letter day at our house. I get the components in the box, and the cats get the extremely exciting packaging materials. Typically there are layers of both white tissue paper and perforated brown kraft paper. Both types are krinkly-- which cats are really into for some reason-- but the brown perforated stuff is a particularly special treat. Our two cats will perfect their running leaps to pounce on it. They will fight over it, where the victor gets to roll around in it and get cozy inside (as JellyBean above has done).
Why? Well, I'm no feline psychologist, but I'll take a few guesses as to why it's so popular: (1) it's easier to sink teeth and claws into than regular paper, (2) it's more flexible, (3) it tears more easily, (4) if you're hiding in it, you can still see out, (5) it's very krinkly, and (6) it slides well on the hardwood floor.
All in all, it's much better than a plain cardboard box, although they often get that too.