One I use alot is www.tvshack.net.. it's a really good website! You can watch movies and tv shows. Click 'video channels' at the top and then choose what you want to watch out of Movies, television, anime, music and documentaries. I've never seen a video on there that doesn't work and they're mostly in really good quality. It doesnt give you viruses either and it doesnt slow your computer down.
But if you want to be certain of no viruses then just go to Youtube and type in what movie you want to watch followed by part 1.. like 'Wizard of Oz Part 1' .. but the problem with Youtube is that you might not find the video that you want to watch.