Gungrave, Darker than Black: Kuro no Keiyakusha Recommendations
If you need action and a deep multiple episode long story to get your anime hard-on, either of these will work. Darker than BLACK contains supernatural action and police-scoured situations with a slowly evolving story, and Gungrave takes the action one step further with intense gun-fights and classic mafia-esque plot development. Watching one will prepare you for the alternative, but make sure you have several months of free time if you plan on watching both @_@
These characters lose everything for the greater good.You honestly can't resist putting yourself in their shoes, and during the end of these shows you'll finally come to an understanding of why they done what they did. Also you'll begin to think to yourself, "What would I have done?"
These anime have completely different settings and plots, but they have a very similar conclusion. So unless you don't want to start thinking seriously about these plots and what they are trying to teach you, then these shows aren't for you.