I always watch:

Dracula(original Bela Lugosi)
Frankenstein(original Boris Karloff)
Bride Of Frankenstein
Horror Of Dracula(Hammer)
Dracula Prince of Darkness(Hammer)
Curse of Frankenstein(Hammer)

One movie I'd like to get to add to the collection is The Brides of Dracula(Hammer)

I also occasionally watch:

Young Frankenstein
Abbot and Costello Meet Frankenstein
Son of Frankenstein(Boris Karloff)
Ghost of Frankenstein(4th movie in Karloff Frankenstein series)
Frankenstein vs. The Wolfman
The Wolfman(Lon CHaney Jr.)
The Mummy(Hammer)
Dracula Has Risen From The Grave(Hammer)