I'm on a roll here. Even more so because these old movies are usually between 70 and 90 minutes long :P Could easily fit two or three of these old movies in the same time it would take to watch one modern epic adventure movie (I'm looking at you Pirates of the Caribbean, The Hobbit, and Lord of the Rings). So the next batch from my list:
4. Frankenstein (1931)
Another iconic movie. This one set the image for what everyone thinks Frankenstein's monster looks like. Even if you haven't seen the movie you're sure to have seen pictures from it or pictures based on it.
5. The Mummy (1932)
Another Boris Karloff movie. Before I started watching it I had a slight wondering, then when the title cards started showing the actors and their characters, I knew. The Mummy film from 1999 that I absolutely love is a remake with spiced up story of this movie from 1932. I figured that out when I saw that Boris Karloff played Imhotep - the mummy himself - with the same name as the mummy in 1999. The base plot of the two movies is the same: a 4000 year-old mummy is exhumed and accidentally awakened, he then tries to get his ancient love back by using a living girl that looks like her, his love betrays him and the living girl is rescued by her boyfriend and the mummy destroyed. Karloff was amazing. In a speaking role like Imhotep he was a lot more charismatic and appealing than as the monster from Frankenstein. His "mummy-stare" is scary and hypnotic at the same time. (I really understand how he got the Hollywood nickname "The Uncanny"). His voice was deep and appealing (imagine a mix of Bela Lugosi and Christopher Lee). I mean, I can see that his looks aren't that amazing, but I sort of fell in love with Karloff here!
6. Creature from the Black Lagoon (1954)
The creature looks like a mix between the Ice Warriors and the Sea Devils from classic Doctor Who.