Yu Yu Hakusho
This show is just so damn good. It's old. Really, really, old. It was released in 1994 and it is still the frickin' king, baby!
The show is just one of the those classics that is so well put together that it stands the test of time. The open credits and the opening music are incredibly good and, for the time, remarkably innovative.
It's also the penultimate buddies hanging out beating the shit out of stuff show... Is that a genre? It should be.
The story follows one Yusuke Urameshi, a deliquent who, in a moment of potential disaster for a small child, sacrifices his life in order to save the child. Yusuke dies, but the story only begins here.
You see, his act of kindness has taken the Underworld by surprise. They don't have a place for him in heaven or hell, yet. So Koenma, son of the Underworld's ruler King Enma, offers him a proposition: return to his body if he can pass a series of test.
The joy of the series is the tournament style root for your favorite characters format. It's sort of like the World Wrestling of anime to an even higher degree than Dragonball Z, only with the melodrama and with far more unique and compelling characters and story lines added.
And lest you think I've wandered down the path of misty nostalgia, remembering the series as being better than it was, let me say that I have watched this series more than once. And unlike the other series I've watched on this list I am more than sure that after a few years I'll watch it a third time.
Do yourself a favor: do some spirit detecting and solve the mystery of why you haven't watched this, yet.