This is the movie that started it all and put serial killer movies on the map. A group of friends go to visit the grave of one of their grandparents and find it desecrated. They stop for a bite to eat at a gas station and eat some meat (not animal!) and encounter a weird hitchhiker (Edwin Neal), who turns out to be one of the members of the cannibalistic family. In one of the more memorable scene Sally Hardesty (Marilyn Burns) is tied to a dinner table next to an ancient looking head of the family--and witness them eating their favorite food. Oh, there's also Leatherface (Gunnar Hansen), who wears a sewn mask of human faces over his own and chases people with a huge chainsaw.
Although this movie spawned over half a dozen sequels and a few remakes, none compares to the original in its intensity, though I do have a soft spot for Texas Chainsaw Massacre 2. Highly recommended.