I was recommended this one and it's really become a great read.
1973, Vietnam - an American soldier goes mad and guns down his buddies. Since then, the only words he has uttered are "Banana Fish"...
Twelve years later, in New York City, police investigate a series of puzzling suicides and a dying man gives a charismatic young gang leader named Ash Lynx a vial of a mysterious substance...
I don't want to spoil this series plot, since it gets real batshit crazy and is soooo good at keeping you hooked and addicted to it.
This is one of those overlooked gems and the whole series was officially published into English. If you are after a really good manga, get this one, you won't regret it. It was very popular in Japan and for good reason.