Squeee! I'm a hoppity-happy IKEA customer! I found Dioder LED strips—four 250 mm segments with nine white LEDs in each, with the included connectors they can be connected in series or in parallel, straight or at various angles, screwed or glued to any flat surface. They seem to be a bit of an experiment, you have to ask a shop assistant to bring them out from their secret store. (And they are a bit expensive at 400 SEK. On the other hand I suspect they will never burn out.)
The Only-begotten Son and I played around with them in various configurations but finally ended up with a quite straight-forward linear strip in the ceiling lighting up the bookcases. Wooh, they are so cool!