This has been making a pretty big splash in our circles lately, so I figure we might as well have a thread for it. Attack on Titan is a fairly new anime, based on the manga of the same name.
Synopsis: Humanity has been driven to the brink of extinction by a race of creatures called Titans. Mindless, huge and incredibly fast and powerful, Titans have only one purpose: eating humans. The remnants of humanity have been driven inside three enormous circular walls in order to survive, armed only with cannons and the "3D Maneuver Gear". Humanity has lived peacefully inside these walls for over 100 years, but that changes one day when the Colossal Titan appears. The story follows Eren Jaeger, a young soldier who despises the Titans for what they have taken from him and all of humanity. His dream is to exterminate the Titans and explore the outside world.
Attack on Titan has a lot of great things going for it: Interesting characters who are developed well, amazing animation, visceral fight scenes, and foreshadowing on the scale of One Piece that leads to some pretty shocking plot twists. (Edit: Oh and the intro is amazing.) Since many people are opting to only watch the anime, please put any discussion regarding the manga, which is far more progressed in terms of plot, in spoiler tags.