Greetings!
I always liked the original Ravenloft line of books and supplements. They are great on providing adventures, interesting NPC's, and all kinds of adventure seeds and advice for running Gothic-themed campaigns. Just stick with the original stuff from the 1990's.
The new products are mostly garbage. The first book a few years back, dealing with Strahd seems cool. Anything more recent though is nonsense.
Semper Fidelis,
SHARK