If you liked the Death Note manga, the Anime-Planet community thinks you'd like:
Kai Eto is the Narcotics Control Division's newest investigator and is quickly partnered together with cold, workaholic Hal Kurabayashi. Their job is to track down drug gangs and they must often work undercover in order to do so. While Hal efficiently locates and arrests his targets, Kai often gets too personally involved and acts based on his emotions rather than on common sense. However it seems that Kai is not all goodness and light, and when pushed to the edge he's taken over by a violent alter-ego which shows no mercy. With Kai and Hal's clashing personalities, opposing methods and secret pasts will these two rookies ever be able to cooperate, or will their inability to see eye to eye prevent them from ever truly working together?
Switch and Death Note are both capitvating detective/mystery stories (Death Note has more of a mystery theme where as Switch centers more around the police) with a dark side to them. To most of society Light seems like a normal, highschool genius, but behind the scenes he is actually Kira, with a goal to kill all criminals. To most people that know Kai Eto, he is a normal, happy-go-lucky kind of guy, but behind the scenes, he has a hostile alter ego that makes him nearly kill people. Both series though also have their little flecks of humor in them sprinkled nicely inside all the darkness and mystery going on. Light and Hal are also quite alike in the respect that they have no intrest in helping the criminals, only bringing them to justice. If you liked either one, you'd be doing yourself a huge favor by trying the other as well.
Both of the main characters in Death Note and The Melancholy of Haruhi Suzumiya have a desire to change the world that they are in. In Death Note, Light decides to change it in a drastic violent, way as opposed to Haruhi who wants to start over completely.