Alice, Sweet Alice (1976) I believe is in the public domain and it's a damn good film.
Same goes for House on Haunted Hill (Not the shitty remake) Little Shop of Horrors (1961)
Nosferatu (1922) Reefer Madness (1938) I know but I laugh my ass off everytime I see that one.
I don't know I can't think of any more off the top of my head have to do a little digging to find a few more but this is a good start.
I think The Trial is a horrible film. Maybe my vote doesn't count because I've never been able to watch too much of it; it bored me stiff. I may be a little harshly critical because I'm such a fan of the story, but, honestly I've sat down to watch it at least three times, and each time after twenty minutes or so I say, "Bah! This sucks!" and turn it off.