1) The Punisher: The archetypal anti hero. He’s unarguably a psychopath yet he kills bad guys soooo…..My favorite run was in the early 90’s when he was the star of three monthlies; punisher, punisher war journal, and punisher war zone.
2) Conan: While he has a code, he is spurred on by soley selfish desires including getting laid, getting loot and beating the piss out of anyone who annoys him. Easily the greatest depiction of the cimmerianin comics, in my opinion, is kurt busiek and cary nords work for darkhorse comics circa 2003, issues 1-28 specifically.
3) Marv: Of sin city fame, he is best viewed in the hard goodbye, the first graphic novel in the seven part sin city series. Writer Frank Miller based his character on Conan set in a modern world.
4) Dr. Manhattan: Not sadistic or even selfish per say but so beyond emotionality or human morality that he can not be considered good or evil. He can be found in “the watchmen” original series by alan moore and is featured from begining to end.
5) Lobo: While he will kill for even slight annoyances, he does have a code. He always finishes a job and he seems to have a strange bond with dolphins, so much so that he will put himself in mortal danger to protect one. Further he seems to love his bulldog and does not premeditate fraggings. He had his own limited series as well as being an occasional advesary of superman.
6) Wolverine in feral form: On occasion wolverine reverts to a bestial existence living only for survival and the hunt. In these times he can be considered neutral as any wild animal acts only in its own self interest.
7) Cerebus: Another character based on Conan, albiet as a parody, is a mercenary wanderer who has many strange adventures. Cerebus the Aardvark takes whatever he can and is even occasionally depicted as a rapist. Cerebus can be viewed in any of his 300 issues all written by the same man constituting a continous 6000 page narrative.
8) Lone wolf: Of Lone wolf and cub, a wandering ronin who walks the path of vengence with a baby he pushes in a cart. Lone wolf and cub was a popular manga redistributed by darkhorse in the 2000’s.
9) Kanaeda: Cool teenage biker gang leader in neo tokyo post world war 3. While initially concerned with getting high, banging his girlfriends and beating up rival gang members, his motivations shift to wanting to save a friend. His story can be found in the six part manga epic “akira” also a truncated anime which also is very good.
10) The Living Tribunal: An all powerful cosmic force for balance in the universe. It will predicate the survival of life whether that means sacrificing millions to save future generations or eliminating something he deems to powerful to exist. He may tip the balance of power towards a seemingly evil entity just to keep absolute power out of the hands of any one being that could then destroy everything. He is most often seen in silver surfer comics, avengers, and massive crossover titles.
Honorable Mention: M.D. Geist, A killing machine with an overwhelming urge to test his strength at the expense of heroes and villians alike. The post apocalyptic world he lives in seems to be mostly made up of assholes so his homicidal urges usually fly. He is also able to control himself to some degree and doesnt go around killing children for shits and gigles, though this is mostly due to the fact that that would present no challenge. He is portrayed as an angel of death and perhaps even neccessary. His exploits can be seen in Koichi Ohata’s complete M.D. Geist or in the anime of the same name.