Having got the Worlds & Monsters book (which reinforces my belief that it's a good time to be WotC's bitch), I was just wondering how the 1e6 different undead species might be categorised.
Body only: skeleton, zombie
Body + animus: wight, ghoul <-- no soul = no superego = kill, kill, kill
Body + soul: vampire, lich, death knight <-- no animus = no bodily desires, only the memory thereof = lots of mechanical, joyless sex with your undead bloodsucking groupies
Animus only: shadow, wraith, spectre
Animus + soul: ?? (maybe ancestor spirits/deathless)
Soul only: ghost
Body only: skeleton, zombie
Body + animus: wight, ghoul <-- no soul = no superego = kill, kill, kill
Body + soul: vampire, lich, death knight <-- no animus = no bodily desires, only the memory thereof = lots of mechanical, joyless sex with your undead bloodsucking groupies
Animus only: shadow, wraith, spectre
Animus + soul: ?? (maybe ancestor spirits/deathless)
Soul only: ghost