A Night at The Roxbury is free to watch (streaming) at Blinkbox.
Ok, so perhaps not the most critically acclaimed film... but one of Will Ferrell's first and has a bit of a cult following. Not bad for a free viewing I thought.
It's worth checking out some of the other tv shows that are free to stream too.
They also have a lot of good codes to buy or rent films for free/cheap - see other deals posted on here.