Death Note games, novels, trading cards and a lot more merchandise besides have spawned from the original manga. There have also been three live-action Japanese movies.
Unfortunately, there have also been copy-cat crimes, which left one man dead in Belgium; and caused the whole franchise to be banned in China.
It's difficult to determine precisely how many copies of the Death Note manga have been shifted around the world. But it must have been a lot. In 2008, before the series was even complete, 26 million of the volumes had been sold in Japan alone.
Beyond that, we must extrapolate from the fact that publishers, Viz Media, are forever mentioning it in the same breath as Naruto, Bleach and One Piece. The recent figures are known for Bleach (75 million in Japan; 2.1 million in North America), so if it is assumed that Death Note is about the same, then those figures provide a ball-park here too.
Viz Productions have sold the film rights for Death Note to Warner Bros. Pictures. Shane Black has been hired to create a live action movie, which is tentatively due for release in 2013. (Very tentatively indeed. It's already been postponed for a year several times, due to contract and script wranglings. But the latest is that it's definitely got the green light now.)
Nearly a decade after Death Note was first serialized, in the Japanese manga magazine Shonen Jump, it continues to attract more fans every day. It's here to stay.