Yu Yu Hakusho is on my top list of animes, it is one of two animes I watch in English and I really like the humour, the characters and how they grow and change throughout the series, the plots are good the only bad actually is that there is only 112 episodes and 19 volumes (which I can finish quite fast) though this is also good as they can't destroy a good serie by being too long. This is a manga/anime based on fighting in all forms and I usually hate those kinds of movies and animes but YYH manage to hook me totally despite that.
Darker Than Black is also very good, I haven't seen it in a long time so I don't really remember the details but I liked the story, the characters and the humour whenever it came. I did buy the series recently so I will watch it again to freshen up my memory:)
Avatar the Last Airbender, it may not be a Japanese anime but it is one of the best animated series I have seen. I love all the characters, it's very funny with great voice actors, great animations, a great story and character developement, the music is also perfect for the settings, if only the movie had lived up to the series:/
Other great animes are DNAngel, Fruits Basket, Tsubasa, Wolf's Rain, Detective Conan, Death Note, Inuyasha (though the anime ended mid season without the great ending the manga had) and Kuroshitsuji. I know I have serious decision problems but this is the best I can do when it comes to narrowing down my favourites:D
Edit: I forgot to add Trigun, a hilarious anime with great characters:)