Samurai Deeper Kyo is a manga series about a young man who finds out that he shares his body with the soul of a legendary samurai. It was created by Akimine Kamijyo and also has an anime version that apparently takes the plot in a completely different direction from the manga.
This is one of those things that I could've sworn I posted about earlier but didn't. I really like the artwork for this series, especially the manga. TOKYOPOP initially released the manga in America but it looks as though Del Rey has the rights now. The anime version was released by Media Blasters a while back and is still readily available.