Some good suggestions, and a few pointless ones. Dunno why anyone is suggesting anything like Madoka Magika and Accel World. Totally not what this dude wants.
I'll give you my personal suggestions since you seem to like the same type of shows that I do (namely Berserk, which is my #1 favorite).
Darker than Black is a really good show, with two seasons plus a short OVA that bridges them together; all dubbed (well). It's definitely meant for a mature audience.
Blue Gender is another great show. It's a bit dated, but definitely worth a watch if you aren't bothered by the older style of animation and you like giant bug monsters and mechs; and can handle a little bit of romance. Honestly, I think it adds a nice touch. In my opinion, this show deserves a full remake with modern animation. It's just good.
Baccano is another favorite of mine. It lacks that dark theme you seem to like, but It certainly has plenty of violence. It's more of a comedy-action than anything, but I think it really tends to appeal to any anime watcher out there. The way it ties things together in the story is pretty neat, too.
Hellsing Ultimate is simply fantastic. It's extremely violent, and definitely redeems the vampire theme. There's only 10 episodes, but they're all nearly an hour long each. I highly recommend this show. You're bound to enjoy it.
Ghost in the Shell in general is just awesome. It's a cyber-punk, neotokyo style series built on conspiracies and some philosophical debate. There's a couple of movies, plus a remake of the original film. Then there's the TV series Stand Alone Complex, which I definitely recommend watching. I believe they also made movie adaptations of the TV series if you find the pacing of the TV series to be too slow because, believe me, it's definitely slow at times. But if you like your shows to have a lot of depth, then you'll love Stand Alone Complex. It's not for everyone though, so don't feel bad if you end up not liking it.
Tengen Toppa Gurren Lagann. I'll start off by saying that this show isn't dark and full of gore and cursing and anti-heroic main characters and stuff. In short, it's nothing like Berserk or Darker than Black. But then again, this show is like no other. It's almost impossible to not recommend this show to anyone who watches anime. Simply because it's one of a kind, and I think literally anyone can enjoy it. I don't think any other show can compare to it. The sheer amount of epic scale this show achieves towards its end is just mind boggling. Just...give it the benefit of a doubt at the very least. It has tons of action, it's funny, it's bad ass, it's even painfully cheesy at times (which is more tongue-in-cheek than anything), but by god is it epic.
Ergo Proxy. Another personal favorite of mine which I'm very surprised hasn't been mentioned yet. Now, this show is extremely slow and can be very confusing on top of that since it has heavy psychological themes. But it's rather dark and definitely has its fair share of violence. Nothing completely over the top, but enough to set a mature theme. A good show to really rack your brain with to try and understand what's going on. And again, simply one of a kind.
Claymore is one show I love and hate. I love the dark fantasy theme it boasts, and the action is good too. But oh my GOD do I hate Raki. If there was ever an extremely annoying, cry-baby main character, it would be Raki. Not even Renton from Eureka Seven was as annoying as Raki. At least Renton actually mans up towards the end. Near the end of Claymore, Raki is sitting in a piss-soaked coward corner crying like a little girl. Oddly enough, they vaguely resemble each other; all that really separates them is the different art styles. But I digress, if you can look past Raki's shenanigans, you'll probably enjoy Claymore a lot. It's a shame they didn't continue the show...I think I remember someone telling me Raki actually mans up later on in the manga and actually starts cracking some skulls.
Well, that's all I have for now. Sorry if my post was gigantic. I figured I'd give you some insight on my recommendations.