Stieg Larsson's The Girl With the Dragon Tattoo has been one of the most popular novels of recent years, and the furor has only continued with the release of the second novel in the series: The Girl Who Played with Fire. His last book (both in the Millennium Trilogy, and forever - Larsson is being published posthumously), The Girl Who Kicked the Hornet's Nest, is due out in the US May 25th.
So what's a reader to do until then? Luckily, there are a wealth of Scandinavian mysteries and thrillers for you to delve into while you wait for your next (and last) Lizbeth Salander fix.
First - don't forget that the Swedish language film of The Girl with the Dragon Tattoo (Män som hatar kvinnor/Men Who Hate Women) is in limited release in the US, and will open April 9 at the Glenwood Arts, locally. Roger Ebert says that "It is destined to be remade by Hollywood. That remake may turn out to be a good film, but if I were you I'd be sure to watch this version." 
As far as books go, two authors that I think compare favorably to Larsson are Peter Høeg and Henning Mankell. Høeg's Smilla's Sense of Snow and Borderliners are two novels I enjoyed as a teen transitioning from Agatha Christie and Dorothy Sayers, hankering for more edgy plots. Mankell's Kurt Wallander mysteries are thrillers with a world-view - my favorite, The White Lioness, combines South African politics with the murder of a Swedish housewife and leads the reader on a chase 'round the world to discover what the connection could possibly be. I'm looking forward to his newest, The Man from Beijing. 
If you're looking for other authors, Becky from the Berwyn (IL) Public Library recommends Asa Larsson and Yrsa Sigurdardottir. The LA Times says that Karin Fossum, Hakan Nesser, Helene Tursten, and Arnaldur Indridason are Nordic writers who are also heating up the scene.
If you have favorites, be sure to share them with other readers in the comments section!
my read shelf: