Never Let Me Go by Kazuo Ishiguro
The Handmaid's Tale by Margaret Atwood
Others came to mind, but they have been already mentioned.
ETA: I've remembered this:
The Perdido Station by China Miéville (I loved it when I was reading it, but I would never read it again because it's too disturbing for my taste)
And
Do Androids Dream of Electric Sheep? by Philip K. Dick (as a movie it was named Blade Runner). I didn't care for it much I admit, but I was very young then.
And Orwell's
Animal Farm.