For almost all of my movies I use Netflix, an on-demand Internet streaming service that's available in North America, South America, Australia, New Zealand, and some parts of Europe. It's the easiest, ad-free service I've found so far and it's one flat rate.
I also use Shush TV to view movies that Netflix doesn't have, and it has new episodes of TV shows that have just aired, while Netflix waits until the whole season is over to stream it. Shush opens pop-up ads in other tabs but it has no in-show commercials.
I don't use Hulu as much (I once signed up for a free trial) but it does have a lot of movies and up-to-date TV episodes. It is also a flat rate, but it shows commercials during the show/movie like regular TV.
Sometimes, I use Putlocker, a free, commercial free streaming website. It can be a little tricky to use, because like Shush, it opens pop-up ads, but unlike Shush, it puts you on the tab and you have to close out of it and go back to the page. It is way more sketchy than Netflix, Hulu, or Shush, but it has a lot of movies very up-to-date and I've used it without problems.