A few years ago my brother got me Buckyballs from woot; a few years later I finally put them down. These things are the most addicting toy your adult self will ever experience.
Sometimes you'll use them to pin the electricity bill on the fridge. Sometimes you'll spend two hours trying to get them all connected in the shape of a diamond. Why would you spend two hours putting them in the shape of a diamond? Well, I don't know, but I've done it multiple times.
Playing with these magnets make you feel like a magician. They are strong enough to magnetize through your hand, desks, sometimes even walls. I know a middle school teacher who has a massive collection of these – confiscated from her unfortunate pre-teens. Its safe to say she never gets bored at work when she can spend some time with these rare earth metals.
When I was in fifth grade I had a project where I was assigned an element from the periodic table: neodymium. I've never thought I'd have this element in my own hands, yet Buckyballs are completely built with the greatest substance known to me. Now, I don't hand out my personal endorsement too often, but these things will make your days. [Buckyballs]