Samurai Champloo + Cowboy Bebop both have the tones you're describing. They're definitely not childish anime, and absolutely contain violence + darker bits depending on which of the two you are watching. Apart from that, the mix of atmosphere + music + story is absolutely amazing. When you get stuff by Nujabes during a big depressing scene in Champloo, or get to hear the opening (Tank) for Bebop before watching some gangster'ish plot showdown, it's pretty sick.


Berserk is pretty much the top dog though. If you haven't, read the Manga. If you haven't, watch the 3 movies ( [bakabt.me] ) etc. Also, if you haven't, watch the Berserk outtakes - i lose my shit every time: [www.youtube.com]




Mixing the idea of dark and violent, but some other stuff you didn't mention - I would definitely give stuff like Paranoia Agent ( [www.youtube.com] ) a try. The idea is a psychological/dark/thriller/surreal mess. You have a breakdown of reality, death, total confusion, you name it.





Similarly, thanks to makers: Paprika ( [en.wikipedia.org] + [www.youtube.com] ).


I'll venture out and pick some others that aren't favorites of mine but are more dark.




Another

It's a sort of murder/mystery/paranormal where nobody knows the exact cause, or the exact person, causing deaths happening in this school. Thus they have to find out who, and needless to say this involves a lot of betrayal.




Ergo Proxy
"The year is 7207 where the world has been ravaged by a cataclysm five thousand years ago, there exists a refuge on this ruined Earth -- a Domed City named "Romdeau," where humans and their android servants, the AutoReivs, live in a state of controlled peace. This construced paradise that houses its wealthy citizens and unfortunate immigrants is ruled by a mayor and his governing council. They demand that complete order and servitude is kept within Romdeau to keep chaos at its gates at bay. However, this utopian landscape is soon shattered by a series of horrifying murders. Re-L Mayer, a female inspector from the Citizen Information Bureau, along with her AutoReiv partner Iggy, are tasked to solve the murder cases. When Re-L and Iggy investigate the latest crime scene, Re-L is almost attacked by a mysterious creature, neither human nor AutoReiv, that is seemingly drawn to her. She begins to learn the truth about the mysterious creatures that are simply referred to as "Proxies" and what they truly are."



Baccano
"During the early 1930s in Chicago, the transcontinental train, Flying Pussyfoot, is starting its legendary journey that will leave a trail of blood all over the country. At the same time in New York, the ambitious scientist Szilard and his unwilling aide Ennis, are looking for missing bottles of the immortality elixir. In addition, a war between the mafia groups is getting worse. On board the Advena Avis, in 1711, alchemists are about to learn the price of immortality. Based on the award winning light novels of the same name, this anime adaptation follows several events that initially seem unrelated, both in time and place, but are part of a much bigger story—one of alchemy, survival and immortality. Merging these events together are the kindhearted would-be thieves, Isaac and Miria, connecting various people, all of them with their own hidden ambitions and agendas, and creating lifelong bonds and consequences for everyone involved."



I mean I could go on but this takes time and I get lazy. Anyway, obviously shit like Ghost in the Shell, Tekkonkinkreet, etc.

Tons of good recommendations in the thread though.