Fullmetal Alchemist. I watched the anime and then eventually got into the comic it was based off of sometime later. A lot of the story is the same up until around the half way point of the anime and then the anime goes off in its own direction.

They are currently on issue 79 or something. Things look like they could be wrapping up soon and it is far better than the anime. It just has a more interesting story as things progress.