Definitely Inuyasha!
One of my first mangas

Full Moon o Sagashite, Inuyasha, Ouran Koukou Host Bu, and Hagane no Renkinjutsushi. Although these are all mangas, I actually watched the anime versions in my childhood and those are what stuck with me all this time. Though for Full Metal Alchemist, I did end up reading the manga and absolutely loved it.

For manga, Black Cat is one of the earliest mangas I read and actually remember. Kimi wa Petto and Banana Fish have also stuck with me.

Quote from Suxinn

Clover is definitely the best manga Clamp ever made, I think. Nothing else really competes. It's hauntingly beautiful even in its inconclusive ending.

I think you meant to link Clover (Clamp) instead (was momentarily confused when I clicked on it and noticed it wasn't by CLAMP).^^

SHIN ANGYO ONSHI: This would definitely fit, the ending is very moving and not to mention the epic death scene.
Saver: Again, really good and the protagonist is my type of heroine.
xxxHolic: Pretty much everything by clamp is worth reading. There is a different full length series that go along with this one, read both and they'll make more sense. The ending was really sad and it is very memorable.

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Ichigo 100% ~ So much teenage feels...

Some of these are impossible to forget because of their length, others left such a deep impression on me I would never forget them, some had such an interesting concept that they would be hard to forget, and lastly some of these I just grew to love.

Boku no Chikyuu o Mamotte
Hikaru no Go
Whistle!
1/2 Prince
Basara
Akkan Baby
Miriam
Yotsubato!
Battle Royale
Glass Mask
Deep Love - Ayu no Monogatari
Full Metal Panic!
Full Metal Alchemist
GTO
Chihayafuru
Tsuki no Shippo
InuYasha
Death Note
Junjou Romantica
Zetsuai
Detective Conan
Rurouni Kenshin
Shingeki no Kyojin
Naruto
Yu Yu Hakusho
Hunter x Hunter
Dragon Ball

Remembrance, a forsaken thing that revokes ignorance and leaves people in doubt, is my only redemption and solace deep within the cascade of white.

The evergreen trees speak of days long past when music mingled with the wind and sweet murmurs brushed our cheeks.

Full Moon o Sagashite, it was one of the first manga's I read, and the characters... I just fell in love with them. It just reminds me so much of my middle school days, and Arina Tanemura's style was a huge factor in my art style.

Bitter Virgin, just a great story overall and I love re-reading it. As someone who rarely reads anything outside of the shoujo genre, this really left an impression on me.

NG Life. Just, again, really great story. Hilarious as well!

In order first ~ last

Vampire Juujikai
Hoshi no Samidare
Watashi no Kyuuseishu-sama
Ubel Blatt

Is this me in a nutshell?
Pretty much.
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Definitely Angel Densetsu, it was the first and still the best manga i've ever read, in the 3-4 years i've been reading manga i've been searching for a manga to rival it, but still haven't found 1, some have come close but nothing has ever compared

stupid photobucket, wanting $400/yr just to display your images

Maison Ikkoku It's a classic and in my opinion Takahashi's greatest work(at least among the ones I read)
Kimi wa Petto Even Though I don't usually read Josei, this is brilliant
and Dragon Ball

For me it's:

Kanata Kara
Eyeshield 21
Akumetsu
Samurai Deeper Kyo
Yakitate!! Japan
Liar Game
One Outs

And some that are going to be remembered:

Kamisama Hajimemashita
Horimiya
Kyoukai No Rinne
Noragami

I think a person's first manga will stay with you forever. My first was rave master and now that I've been reading manga for 10 years, it probably has a lot of flaws but in my mind it'll always be perfect.

It's forever Basara :3

Berserk
Angel Densetsu

There are a couple of more but these two, masterpieces