This is a list of mangaka whom I admire. In no particular order:

Takehiko Inoue (Vagabond, Real, Slam Dunk)

When I first bought Vagabond, it was actually a mistake. I'd wanted to get Blade of the Immortal, which I'd read and heard about, and I picked up Vagabond thinking it was the former (it didn't help that the titles were in Chinese, and the copy was shrink-wrapped). Nevertheless, I found the art to be superb and of a realistic style. Of all the mangaka, Inoue is probably the one that had the most influence on me.

Hiroaki Samura (Blade of the Immortal, Emerald)

Blade was unique in every way when it first came out. On first glance, the art seemed sloppy, but the raw pencilled look greatly appealed to me. Action is nicely rendered; sometimes it feels as though you're looking at a sequence of movie stills. A pure work of art, and worth every cent.

I recently discovered a HK manhua (C.A.T, by Fung Chin Pang) that managed to imitate his style perfectly.

Nobuhiro Watsuki (Rurouni Kenshin)

Kenshin counts as the first series that I bought, and it was on account of the anime (then showing on AXN). The experience of reading the manga didn't quite match up to the experience of watching the anime, so on that point I was sorely disappointed (the manga also contained some bits that I found distasteful).

What I did like about the manga were the special 1-page commentaries inserted in-between chapters that detailed Watsuki's conceptualization of the characters. His influences were pretty broad (including from Marvel Comics, which I could relate to).

The convention of naming sword/striking techniques is strongly reminiscent of the wuxia genre, and I sometimes wonder if there is an awareness/influence of wuxia in Japanese pop culture. Anyway, for a length of time (this was before I discovered Inoue), I copied Watsuki and drew all my characters with pointy chins.

Tsukasa Hojo (Angel Heart, Family Compo)
Masashi Kishimoto (Naruto)
Tohru Fujisawa (Great Teacher Onizuka, Tokko, Rose Hip Zero)
Tsutomu Nihei (Blame! Academy, NOiSE, Digimortal, Biomega)
Usumaru Furuya (Jisatsu Circle)
Jiro Matsumoto (Freesia, Keep On Vibrating, Uncivilised Planet)
Tsutomu Takahashi (Jiraishin)
Hiroya Oku (Gantz, Zero One)
Shimizu Yozo (Wonder School Boy)
Chan Mou (The Ravages of Time)
Youn In-wan/Yung Kyung-il (Shin Angyo Onshi)
Andy Seto (King of Fighters Zillion)