Horror of Dracula, 1958, a Hammer film. You may have noticed that I have not selected the original Dracula with Bela Lugosi. This is because I consider it more of a "classic" film than a B-movie, and frankly, it's kinda less enjoyable. Horror of Dracula stars Christopher Lee as the titular vampire and Peter Cushing, and though Bela Lugosi's performance is magnetic, Lee has his own version of magnetism. And it's fun to watch Peter Cushing as a super-serious, super-British Van Helsing.
The Wickerman, 1973, also a Hammer film...but a really weird one. Super pagan. Super hippy! Considered "the Citizen Kane of horror movies" by Cinefantastique, apparently. Christopher Lee was a Hammer Films regular by now and really wanted to get away from the usual kinds of horror film roles he was cast in. This certainly fit the bill. Do NOT bother with the 2006 remake with Nicholas Cage, unless you have time to spare and want a (possible) laugh.
Strictly speaking, The Wickerman is too well regarded to be considered a B-movie, but it's just so odd, I can't help but categorize it as such!