I hope this is the right section to ask (it is called "content for your site", after all. I'm looking to start a website similar to rottentomatoes.com. Does anyone have any ideas on where I could get content for it (trailers, movies in production news, stuff like that)? Free or fee-based, I need to know what's available out there.
Don't even think about it. Sorry to sound so abrupt but contrary to what you might think, making a site like RT or IMDB is a bad idea. Apart from the fact that both are considered high quality brands (and you will find it VERY hard to convince people to move from those ), the real problem will come into the cost factor. Making a website that showcases movie releases will literally cost you millions of dollars every single year. As has been pointed out above, you'll have to pay royalties for every trailer, every image, every "still" from the set, every publicity shot. In addition to that, getting the latest news isn't going to be something you can just buy. In cases like RT and IMDB, they have journalists who get the news exclusively for those sites (in addition to sistering with organisations like the Associated Press - for which they'll be paying thousands a year for a license to their content). Essentially, starting up a movie website to compete with the established and reliable brands is going to put you millions out of pocket and you probably won't even get near enough of an impact to generate the revenue to cover such a scheme.
You need to pay royalties for movie trailers. Its not free (sorry!)
As far as news, sites like rottentomatoes have their own writers/journalists.