As part of YouTube's entry into the online movie-streaming business, it has created something called OpenFlix -- a collection currently boasting 670 free, full-length movies. As far as I can tell, they're all public domain films -- but some are classics, and worth a look. They all have ads at the beginning and periodically throughout the feature. Many of these are also available (commercial-free, but not in the convenient YouTube format) at Archive.org's Moving Image Archive.
Night Of The Living Dead... READ ON