Manga artists for me.
Nobuhiro Watsuki (Rurouni Kenshin) - Obviously since he created Sagara Sanosuke, my favorite anime and manga character and where my net name comes from lol! What I love about him is how much he loves a lot of the same things I like, Marvel, DC, Capcom, SNK, Evangelion, etc. You can see it in many many of his character designs. His new work Busou Renkin is also great and he did character designs for Samurai Showdown V too. 
Hirohiko Araki (JoJo’s Bizarre Adventure) - Hecould do an American comic book no problem, I’d love to see that.
Tetsuo Hara (Fist of the North Star AKA Hokuto No Ken) - I’m a HUGE fan of Fist.
Katsuhiro Otomo (Akira) - He is just amazing at drawing buildings and machinery.
Akira Toriyama (Dragon Ball) - Much like others have mentioned. If you get a chance look at his manga and the way he draws mountains and clouds, any kind of scenery period! The anime doesn’t do it justice. Though I don’t see how they could otherwise they’d still be drawing the show lol! Big up to the Super Dragon Ball Z game for trying to incorporate the look of the manga instead of the anime!
Ryoichi Ikegami (Mai the Psychic Girl, Crying Freeman, Spider-Man manga) - Another artist I can see doing an American comic very easily. Hell he already did with the Spider-Man manga which is just great!
Kentaro Miura (Berserk) - Man this guy does an insane amount of detail.
Rumiko Takahashi (Ranma 1/2, Inu Yasha) - Admittingly I like her story telling more than her artwork but her drawing isn’t bad either. She’s one of the greatest writers on the entire planet IMHO so I just have to give her a nod.
Eiichiro Oda (One Piece) - I love the way this guy can do some crazy foreshortening and make it look believable. I’m still suprised that they are able to make that work in the anime too. This is actually very hard for an artist too accomplish and make it look good.
Masashi Kishimoto (Naruto) - Obviously I have to mention him lol! His character designs always look better than the anime versions. It’s hard for me to put my finger on why but I think he draws children a little smaller than they are in the anime.
Itoh Mami (Various Capcom manga) - She’s my favorite Capcom manga artist, mainly because she’s touched everything from SF2, SFA, to DS 1, 2, 3, and even Warzard AKA Red Earth! And I just love her drawing style.
Masahiko Nakahira (Various Street Fighter manga) - My second favorite Capcom manga artist but he only deals with Street Fighter. Still it’s amazing how much influence his manga had on the games - He created Satsui No Hadou Ryu (AKA Evil/Dark Ryu) and Karin; Capcom liked them so much they incorporated them into the games. 
Syuun Matsuena (Shijou Saikyou no Deshi Kenichi) - I got into checking out this manga recently after playing the game and watching the anime lol! He has some great character designs and the fight scenes are pretty awesome!
Kia Asamiya (Silient Mobius) - He did Batman Child of Dreams!!! And he drew Uncanny X-Men too for just a bit. He almost did a back up Chun-Li story for Studio Udon but sadly things didn’t work out, ah man I would of loved to of seen that but ohs well.
And I know I forgot a crap load of people ack… 