im a movie addict as well but limited to certain genres, so my pool of knowledge is more like a monoculture than a well developed eco-system
so i prefer horror movies as well, but none of the american made ones (most of all when it came to re-makes of asian originals) impressed me at all
there's a list of must-see's like the ring (of course), audition, ichi the killer, battle royale, men behind the sun, kairo, versus, ...
i came into this whole field due to my exex who's more than knowlegable to the field and would be able to add to this list
we started out with the italian movies directed by men such as licio fulci and dario argento or others, examples are: cannibal ferox, cannibal holocaust, last house on the left and many more i cant remember off hand but am able to list from my vhs collection at home
there's also this whole movie collection from guinea pig movies which are apparently very gory but i havent seen (yet), like mermaid in a manhole, flower of flesh and blood, the devil's experiment, and more
recent movies which were ok are: 1408, the number 23 (although getting a little too paranoid and who taught those guys math?), sawI (sawII already tended to address only main stream audience), the host
the WORST horror movies ever are the american remakes of asian movies (like the grudge or the ring or even pulse) and dont even get me started with hostel
there's also other movies i could recommend not belonging to this particular genre but impressed me such as pan's labyrinth, a scanner darkly, night watch/day watch (russian productions) ...