I'll second Trinity Blood - and since it's set to debut on Adult Swim beginning September 9th, it's a great way to check out the series before you commit to buying it. Personally, I like it because of the awesome visuals which are very stylish and well animated. Though I also dig the storyline and characters as well. If you're into vampires, apocalyptic anime, or just "darker" anime in general - check it out.
Also, I highly advise checking out "Judge." It's a little one-shot OVA, about 45 min long or so, about the Judge of Darkness, who upholds the laws of the dead and seeks justice for those that can't find eternal rest. It's quite a bit older, but I love the concept and the story is pretty well exectued, IMO.
That would be my .02
