The Labyrinth, a
storehouse of files related to Hexen II (wads, utilities, levels, etc)
Deadmeat's
BSP Hexen 2 Entity Tutorials , currently covering text messages,
rotating doors, translucent windows and spawning objects from other
objects. Intended for BSP but generally useful.
EutecTic's
H2 entity list , zipped. Almost all entities covered, text format.
This is the original entity info resource, and still all there is for
a few advanced ones such as func_angletrigger.
Inside 3D's HexenC
coding info (where to get the source, getting started, tutorials).