silly putty (or in dire times, ticky tack). there are just too many fun things to do with it. sculpt it. string it out like taffy. pull on it hard and snap it (great stress relief). good silly putty even bounces!

quill and ink for writing. It's fascinating because there's some actual "talent" involved in writing, instead of merely scrawling out words. (and quills look damn cool). they're also wonderful to draw with as the thinkness of the line can be controlled.

dry erase markers are much fun. you can draw on nearly anything--good plastic surface, window, monitor and instantly remove it and do it all over agian.

puzzle toys such as puzzle rings, the little nail puzzles, etc. rubinks cube technically fits here, but is too "orderly" and complex. The things are so irritating because them seem so simple, adn it's maddening to let a little hunk of metal get the better of you!

those little nail board things, the ones with hundreds of tiny blunt nails that you can leave imprints and impressions of things in by moving the pins up or down by squashing objects on them.