I remember having this same conversation with my dad when the library he worked at had a sudden windfall and they could buy a whole bunch of books at once. I think they were considering graphic novels, but experience had taught them that the boys would steal them.

For some reason, the Guinness Book of World Records was inordinately popular (to the point where it was also stolen.) The younger boys (the kids were aged 10-18, more or less) also seemed to like books about how things work, or the DK Eyewitness books and such things.