The internet is filled with information on BSP trees in 2 dimensions (i.e. raycasting, all walls are parallel). Does anyone have any links or know of a book that discusses BSP trees in 3 dimensions?
If you are not afraid in going deep into the code, you can take a look at the Quake3 source code using 3D BSP. You can be sure it is well coded, at least for a real time, game oriented application.
Wikipedia should be enough if you need only high-level concepts.