Where to watch movies online for free?

There's quite a few movies available to watch on YouTube, such as older films where the copyright has expired (search for "public domain movies"), or smaller indy films where the makers have decided to show it for free.
Watching copyrighted movies online for free using dubious sites would be illegal, and I'm sure you wouldn't be interested in that now would you?
Also many of the dodgier sites are loaded with pop-up ads and malware that can infect your PC.

Crackle