There are some twist endings that you avoid talking about because you don't want to ruin them for other people, but then there are those that are so well-known they have become cliches. For example, even without seeing Soylent Green, you probably already know that "Soylent Green is people."
If you're not afraid of spoilers that everyone already knows, you'll probably dig Flavorwire's great list of the best movie twists in cinema history -from Planet of the Apes to the Sixth Sense.