進撃の巨人 by Isayama Hajime
Only 4 volumes of this manga has been released and each volume sold more than 1 million.
(only 50000 was printed during its initial release)
Summary: Humanity has gone almost extinct since the rise of the Giants. All the remaining mankind's are living inside a Great Wall that protects human from Giants. The story revolves around the protagonist who wants to go out of the wall by joining the research sqaud.
This manga seems really promising. I like the setting and its atmosphere around the grim future human's are living in a world where human's are just a food for Giants.
–- Update From New Post Merge ---
one interesting Fact:The author of this manga initially brought it to JUMP, but the editor told the author to bring "JUMP" rather than a "MANGA" so the author went to Shonen magazine and it became a huge success.