YouTube is well-known for its short user-made clips, but the site also hosts numerous free movies as well.
YouTube Screening Room is a channel dedicated to short independent films. Four new films are featured every two weeks, so the selection changes often.
YouTube Movies offers full-length modern films, approved and hosted by the site. Use the category filter to select only free films on the site and start watching.
Note that not all free movies are suitable for all audiences!