I love In the Mouth of Madness and I confess it contributed to my mild Sam Neill phobia (which started with Event Horizon -- heck, even the character he played in Jurassic Park was kinda creepy.) I haven't seen Prince of Darkness or nearly as many of Carpenter's oevre as I should have. Obviously I've seen the top classics like Halloween, The Thing, The Fog, etc.

Carpenter's segment for Masters of Horror, Cigarette Burns, is very MoM-like--
if you haven 't seen it. Oh boy!