You can think me as beginner to manga culture, so I want to know classics of manga world so please let me know many classics!

[color=blue]MILESTONES[/color]
1st: Death Note

3x3 Eyes
2001 Nights
AD. Police
Akira
Appleseed
Area 88
Ashita no Joe
Astro Boy
Bastard!!
Berserk
Black Jack
Captain Harlock
Captain Tsubasa
Cat's Eye
Crying Freeman
City Hunter
Cutie Honey
Cyborg 009
Devilman
Dominion
Doraemon
Dororo
Dororon Enma-kun
Dr. Slump
Dragon Ball
Dragon Half
Galaxy Express 999
Gegege no Kitarou
Getter Robo
Ghost in the Shell
Giant Robo
Golgo 13
Guyver
Harenchi Gakuen
Hokuto no Ken
Jojo's Bizarre Adventure
Jungle Emperor Leo
Kamen Rider
Kinnikuman
Kochira Katsushikaku Kameari Kouenmae Hashutsujo
Lone Wolf and Cub
Lupin III
Mach Go Go Go
Maison Ikkoku
Mazinger Z
Miss Machiko
Nausicaä of the Valley of the Wind
Nihon Chinbotsu (SAITO Puro)
Oh! My Goddess!
Osomatsu-kun
Ougon Bat
Outlanders
Parasyte
Princess Knight
Ranma 1/2
Saint Seiya
Shounen Tantei Rock Home
Skull Man
Space Adventure Cobra
Space Battleship Yamato
Terra e...
Urotsukidouji
Urusei Yatsura
Violence Jack
Warau Salesman
You Are Under Arrest!
Zatoichi

And, that should cover most of the classic up through the 80's, and others can add to the list any significant ones I forgot. However, there's some that I intentionally left out, such as Slayers and Legend of the Galactic Heroes, because those series were originally light novels, NOT manga.

[img]http://www.dragonflycave.com/wpay/mew.gif[/img]

New Treasure Island is a necessity if you're looking for series with a big impact on manga history. Note that the scanlated version was from the 80s reprint and has a different ending than the original (as published).

If you're open to reading BL, Heart of Thomas was perhaps the first to be serialized. If not, you should still read some Hagio Moto works, such as They Were Eleven or Gin no Sankaku. Also, the stories in A Drunken Dream and Other Stories are considered to include her best oneshots, so get that if you can.

Thank you!

[color=blue]MILESTONES[/color]
1st: Death Note

Everything by Osamu Tezuka. Seriously, this guy influenced everything. Like, the other posts mention his works but still don't encompass all his most important works.

Year 24 Group

I need more please!

[color=blue]MILESTONES[/color]
1st: Death Note

Sorry this is kind of a jumble but...
If you are interested, while not classic in the traditional sense, but:

Works by ITOU Junji - most of his work is iconic, and amazing for the horror genre

Works by CLAMP - some their notable work includes: xxxHoLic, Chobits, Tsubasa - Reservoir Chronicle

While the anime got a lot of credit, the Jojo Series, by ARAKI Hirohiko

Works by TOGASHI Yoshihiro - specifically Yu Yu Hakusho, be aware of if you start HunterxHunter its been on haitus more then its been published at this point due to chronic health problems, but still a solid series

Works by INOUE Takehiko - Slam Dunk, Vagabond, Buzzer Beater (Buzzer Beater is a personal fav of mine)

Works by URASAWA Naoki - Monster being the most notable

Due to the prolific length and it still going: Hajime No Ippo

Other Recommendations (yea no clue if these even fit, but good series):
Initial D
Skip Beat!
Hellsing
Sailor Moon
Fullmetal Alchemist
Mushishi
GTO
Rave Master
Rurouni Kenshin
Fruits Basket
Air Gear
Eyeshield 21
Trigun Maximum
Ouran High School Host Club
Sailor Moon
Claymore
Inuyashiki
Vinland Saga

Thank you I will bump the topic when I read all of them.

[color=blue]MILESTONES[/color]
1st: Death Note

Hello, there!
I also want to recommend some of my favorites (that haven't mentioned yet):

Note : the year is varied from 1990's to 2000's (under 2010's).

Shoujo
Basara -- one of masterpiece in shoujo field. Art is messy but getting better with times.
Akazukin Chacha -- fun and light reading.
Boku no Chikyuu o Mamotte

Seinen
Dragon Head
Ping Pong
Yokohama Kaidashi
Piano no Mori
Emma
Liar Game
Historie
Blade of Immortal
Planetes
Team Medical Dragon
Subaru
Cesare
Homunculus
ES
Dogs
Kurosagi Corpse Delivery
Saint Onii-san

Hope it helps. Enjoy!
If you need it more specific, almost high-rating series section from this website is worth it.