This link will take you to the 1922 Nosferatu online:
http://video.google.com/videoplay?docid=-6185283610506001721
Or Dracula (1931) starring the wonderful Bela Lugosi
http://video.google.com/videoplay?docid=-1951778873752026088&q=source:007259498880564830540&hl=en
And The Cabinet of Doctor Caligari (1919) opens here:
http://video.google.com/videosearch?q=doktor+caligari&hl=en&sitesearch
Choose the second one on the list.
Worth scanning for some early codes and conventions.
This scene from Frankenstein (1931) is illuminating:
http://video.google.com/videosearch?q=frankenstein&hl=en&sitesearch=&start=10
As is the 1954 classic Them!
http://video.google.com/videosearch?q=them&hl=en&sitesearch=
Also available online is Night of the Living Dead (1968) George Romero's zombie horror classic:
http://video.google.com/videoplay?docid=-2956447426428748010&q=&hl=en
And the truly wonderful and bizarre Freaks (1932) directed by Todd Browning (also dir. Dracula 1931) that uses real deformed actors in various roles based around a circus sideshow:
http://video.google.com/videoplay?docid=6355110065089064433&q=&hl=en
Science fiction found it's nadir in the laughably awful - yet strangely marvellous Plan 9 From Outer Space (1959) - if you've seen Tim Burton's Ed Wood, starring Johnny Depp (one of my favourite films!) it's based around it:
http://video.google.com/videoplay?docid=-7038656109656489183&q=&hl=en
If you like your fears a little melodramatic why not indulge in some Reefer Madness (1936):
http://video.google.com/videoplay?docid=-6696582420128930236&q=source:007259498880564830540&hl=en
