a beautiful basic system, fnp modular shelving by moorman is a well known standard in germany. i'd love to see it more here in the states. there are quite a few of this type of system from companies in europe, but this one seems to me to be the best. the montana system out of denmark (not slotted, but also european) also presents some very nice possibilities.
anyone who has seen the bookend selection at, say, barnes & noble is aware that most of the bookends out there are massive, sculptural productions of polar bears and ships and globes. even looking for simple ones at an office supply store will usually yield something that looks like a hand or gigantic paper clip. luckily, I work near muji and so was able to bring home these barely-there bookends, which get the job done without looking like dobermans.
i also came across this lovely adjustable bookend recently on manufactum, a german site that stocks simple everyday classics.
a few more from manufactum.