I'm an old school horror nut too. It's hard to pick favorites when you're talking about movies that span from the '20s to the '70s (my very large sweet spot), and that cover so many styles. I get as much enjoyment out of a bizarre piece of '70s cheese like SCREAM AND SCREAM AGAIN (which I finally watched for the first time last night) as I do a classy Val Lewton mood movie.
Some Hammer favorites - HORROR OF DRACULA, BRIDES OF DRACULA, REVENGE OF FRANKENSTEIN, FRANKENSTEIN MUST BE DESTROYED, TWINS OF EVIL
Some Universal favorites - BLACK CAT, BRIDE OF FRANKENSTEIN, SON OF FRANKENSTEIN, THE INVISIBLE MAN, THE WOLFMAN
I've never seen an Amicus horror anthology I didn't love.
Some honorable mentions that maybe don't get talked about as much:
DOCTOR X - Love the weird atmosphere of this one, made more strange by the early two-strip color. "Synthetic flessshhhhhh!" I'm usually not crazy about wise-cracking comic relief in these kinds of movies, but Lee Tracy's fast-talking slapstick reporter adds a nice lightness that actually compliments the darkness really well, rather than undermines it.
THEATRE OF BLOOD - There's never been a more perfect pairing of movie and lead actor.
DR. JEKYLL AND MR. HYDE (1932 Frederic March version) - Saw a screening of this a couple years ago at a downtown theater as part of a horror double-feature. March's performance as the debauched Hyde was so effective that it still had the power to make the audience uncomfortable.
RETURN OF THE VAMPIRE - I like this one mostly for superficial reasons. It goes all-in on the cliche Halloween look, with all those fog-laden cemetery sets, Bela Lugosi as a Dracula-like vampire, and a werewolf thrown in just because.
THE RAVEN (AIP version) - When I saw this the first time I could not get enough of Peter Lorre getting enraged and yelling at Jack Nicholson.
BLACULA - Finally saw this last year, was surprised how good it was. I was expecting a tongue-in-cheek blaxploitation horror spoof, but it actually worked really well as a horror movie in its own right. William Marshal takes his role as the tragic vampire seriously, and gives a great dignified performance that evokes the audience's sympathy one minute, and horrifies them with his savagery the next.
I could go on like this all day.