Yu Yu Hakusho: Ghost Files

If Yu Gi Oh can be considered the companion piece to Pokemon, than Yu Yu Hakusho could be considered as a suitable companion piece for Dragon Ball Z.

The story concerns Yusuke Urameshi, a teenage boy who dies and comes back to life in an unusual twist of fate. As a side effect, he develops unusual psychic powers and is appointed as the spirit detective of the Earth, defending it from various demonic creatures.

The fights are more interesting than in DBZ, they really keep you on the edge of your seat, and they generally aren't too long and drawn out. The characters powers are also more entertaining and believable at once (i.e. They only get achieve levels capable of destroying the Earth towards the end, rather than in the very first saga, therefore, they usually must rely on strategy).

The characters are realistic and diverse, at least compared to most other shonen anime. They can be despicable, lovable, heroic, tragic and everything else, often all at once.

Of particular interest is the Chapter Black Saga, which tells the story of Sensui.