OK so, I've seen quite a few Anime's in my time such as Gantz, Master Of Martial Hearts and most if not all of the Studio Ghibli films! So I'm looking for more anime's like that! On a different note but not enough to warrant a separate thread lol, a friend and I are looking for some "Scary" horror or Sci-Fi anime's to watch in a few weeks. Thanks for any suggestions bro's!

I have an answer for both of your questions. Serious: Clannad, hands down. I love this anime to death, when i first saw it i was in awe and amazement, blood freezingly amazing. There are funny parts but there are serious parts, and it makes you fall in love with the main characters. My layout is actually Clannad. No spoilers.

Horror: 11 Eyes maybe I've only seen the first episode and i was only half paying attention, but if you want an anime that you'll feel and it has "scary" parts in it then check out Hell Girl. there are 3 seasons to it only season 1 is english dubbed the other 2 are subbed. I really liked that anime, i think you may as well.

Weird: i know you didn't ask for weird but i recommend Oreimo, or Ore no Imouto. They're the same differently named depending on what site to look them up on, i dont think either of them are english dubbed *i dont remember sorry* but once you get past the weirdness of it i think you'll like it.

Elfen Lied is prob one of the best serious animes. If you haven't seen it, I definitely recommend it.
It is one of, if not my favorite anime.

I would suggest the Evangelion movies or the original anime series if you want something more retro.

I like Horror 11 Eyes, I would recomend it if zeross did not say it. But anyways, it is pretty serious.

I'm with vanelan. I can definitely recommend Elfen Lied. If its serious that you're looking for then this can definitely provide you with it. It's not of my favourite amines, but it's really good and I recommend it.

Suitedsnake : Like a lot of the others here I'm gonna go with Elfen lied which is German for "elf song" funny name given that this show might make some.... Less strong stomached of us wanna stop, But if you're looking for serious this is what you want, Although be warned this show is TV-MA so if you're underage and living with guardians you're gonna want to make sure they're okay with it first... Or not.

Another slightly less serious and a lot less Gory and nudity filled show that I would recommend is Soul Eater, It really is worth a shot. Enjoy yourself man, You've only got so long on this world.

I'd like to choose either Death Note, Code Geass, or 11 Eyes. Those were really good anime to add to the card as well. I'm sure you know these already, but I seem to keep finding the anime that is pure comedy. Hence layout

I like DBZ. Its looks like a very serious anime. Becuase it mainly based on fighting and all that.

Suitedsnake : Higurashi No Naku Koro Ni? Shaman King? Death note?
There are lots of anime you can watch that is serious and scary.
I would start of with Death Note.
So interesting. 

Well, Naruto gets pretty serious at times. It definitely gets emotional. Trust me. It will take us a lot of your time. There are 230+ episodes in the original. Then, there is a 2 year story line gap while Naruto is away training, and then Naruto Shippuden came out, and it gets really serious. Trust me... start with Naruto, not Shippuden. 

Try Oban Star-Racers.  I cried a bit during the show, I admit.  The characters are well developed and the animation is AMAZING.  It used to be on Netflix, but you could find it on Amazon, I'm sure.

If you want something to pull at your heartstrings and make you laugh at times Try Clannad  and then Clannad After Story, the after story will really pull you in and jerk those tears out of your eyes so grab a box or two of tissues. Well at least it did me. Good luck finding a serious anime there are lots to chose from.

Naruto is a good one. My friends watch it and it has a long story. It may get a little complicated ut it is still a good anime to watch.

all the .hack's (id start with //sign) i have started watching it. its a bit confusing at first. just saying but "the world" is an online game that sold millions. it seems a bit silly at first, but, it gets serious over time. fake wings is my favorite song in the serise.

To be honest most anime that are really popular are based for preteens which in China and Japan are equivalent to 16+ in the United States. So already knowing that you asking for more "Serious Anime" is a little hard to come up with since most anime is for an older audience anyways. So I will lay out the list I came up with and pretty much give a short summary of the storyline and why I enjoyed it. I am sure you just want some Anime that does not have a childish feel to it which is understandable since I personally love mainstream Anime and Manga but because of how they are trying to market to younger audiences despite the different age ratings my interest in most of them are fading very quickly, especially with the Naruto series which to my surprise was only marketable to children and young adults.

1) Death Note. This anime is a little darker than others which is a favorite to many. the summary of this anime is as follows:

"Death Note(?????Desu N?to?) is a Japanese manga series created by writer Tsugumi Ohba and manga artist Takeshi Obata. It centers around Light Yagami, a high school student who discovers a supernatural notebook, the titular death note. This notebook grants its user the ability to kill anyone whose name and face they know. The plot follows Light's subsequent efforts to exterminate criminals and "bad people" using the notebook, and the attempts of the detective L to stop him."
(Taken from Wikipedia)
So as you can tell this series has a darker feel to it from other more mainstream and popular anime and manga. This is definitely a recommendation by an anime and manga lover and in general is considered the best anime ever made even though it only goes for about 15-18 episodes.

2) Black Lagoon though I have not personally watched this series I have only heard great ratings about it. This is the summary as follows:
"The story follows a team of pirates/mercenaries known as Lagoon Company, that smuggles goods in and around the seas of Southeast Asia in the early to mid 1990s.[1] Their base of operations is located in the fictional harbor city of Roanapur in southeast Thailand (somewhere in the Amphoe Mueang Trat district, likely on the mainland north/northeast of the Ko Chang island or on the island itself).[2] They transport goods in the 80-foot (24 m) Elco-type PT boatBlack Lagoon. Lagoon Company does business with various clients, but has a particularly friendly relationship with the Russiancrime syndicate Hotel Moscow. The team takes on a variety of missions—which may involve violent firefights, hand-to-hand combat, and nautical battles—in various Southeast Asian locations, even going as far as Phu Quoc island of Vietnam and when not doing much, the members of the Lagoon Company spend much of their down time at The Yellow Flag, a bar in Roanapur which is often destroyed in firefights."
(Taken from Wikipedia)
So it has a little darker ring to it and it has great ratings so I would give it a try especially since it only ran for about 24 episodes.

3) Berserk. It has a very long manga series which I would suggest reading if you enjoyed the anime which covers the first arc with 25 episodes. It is known for its violence and it is also pretty well rated. This is the summary:
"Berserk(?????Beruseruku?) is a manga series written and illustrated by Kentaro Miura. Set in a medievalEurope-inspired fantasy world, the story centers around the characters of Guts, an orphaned mercenary, and Griffith, the leader of a mercenary band called the Band of the Hawk (???Taka no Dan?). Themes of isolation, camaraderie, and the question of whether humanity is fundamentally good or evil pervade the story, as it explores both the best and worst of human nature. Both the manga and anime are noted for their heavy violence."
(Taken from Wikipedia)
So maybe you would like to give that a try?

4) Hellsing. Not only is it loved by almost all anime and manga fans but it is more of a mature theme and story with quite a lot of great action and violence. This is the summary:
"Hellsing is named after and centered around the Holy Order of Protestant Knights, originally led by Abraham Van Helsing. The mission of Hellsing is to search and destroy those that threaten Queen and Country from the undead and other supernatural forces of evil. This organization is currently led by Sir Integra Fairbrook Wingates Hellsing, who inherited the leadership of Hellsing as a child after the death of her father. She witnessed his death which turned her from a once innocent and shy little girl to a tough and deadly force. She is protected by the faithful Hellsing family butler and former Hellsing "trashman" Walter C. Dornez, a deadly foe in his own right, and Alucard, the original and most powerful vampire that swore loyalty to the Hellsing family after being defeated by Van Helsing one hundred years before the story takes place. These formidable guardians are joined early on in the storyline by former police officer Seras Victoria, whom Alucard turned into a vampire. She is mostly involved for satire and comedy and beauty as a new vampire trying to learn a new lifestyle.
As the scale and frequency of incidents involving the undead escalate in England and all around the world, Sir Integra discovers that the remnants of a Nazi group called Millennium still exist and are intent on reviving the Third Reich by creating a battalion of vampires. Millennium, Hellsing, and the Vatican section XIII Iscariot clash in an apocalyptic three-sided war in London, and Millennium reveals its true objective: to destroy the vampire Alucard, ending a feud begun during World War II."
(Taken from Wikipedia)

So I hope this list sparked your interest and offered you what you were looking for.

Steins Gate an AMAZING anime you should definitely watch it 

Give Ghost Hound a try, its got some super natural feel, along with some scary scenes mixed in with sci-fi as well.