Yes, they are usually PPV streams, but there are some free. In addition, Amazon Prime customers have access to a much larger library of free films. Prime accounts give you free shipping on eligible orders as well. There's a one month free trial available. Plus, you can apply for a free Prime account if you are a college student.
Flixter is a paid V.O.D service but you get one free movie just for signing in for your facebook account. The movie they give is owned by you and can be watched across multiple platforms supporting the UltraViolet system. You get another free movie for "Liking" and Tweeting Flixter. If you send invites to your friends they'll get a free movie and you'll get another for every friend who accepts. The catch? You don't get to choose the movies. Some are good, but some are irrelevant.
Vudu has lots of promos to get free credits when you first sign up. You also get credits for referring friends. This month, you get a free movie for linking your Vudu account to a free UltraViolet account through their website. If you try their disc-to-digital program at a cost of $2.00, you get another 5 free movies. All of which you own. The catch? The selection is limited and the additional 5 movies are in a bundle. There were 3 bundles to choose from when I tried it.