Since I don't have a ready-made list of those, I'll change things up a little and give you my list of favorite artists who worked on my favorite GN's. Note that I'm mainly a reader of Euro GN's, as you'll see: (click for samples)
P̲i̲e̲r̲r̲e̲ A̲l̲a̲r̲y - Stylish, kinetic work featuring figures with unusually expressive, even eccentric faces. His cartoony style works surprisingly well for historical fiction, which Alary demonstrates again and again. [Don Vega, B̲e̲l̲l̲a̲d̲o̲n̲n̲a̲***☑***, Conan the Cimmerian, SinBad, Silas Corey]
D̲e̲n̲i̲s̲ B̲o̲d̲a̲r̲t̲ - Just as Alary is a master of motion, Bodart is a master of bringing stationary figures to life, particularly in his Victorian-era works. [G̲r̲e̲e̲n̲ M̲a̲n̲o̲r̲***☑***, <many more>]
I love Stitches by David Small, Heck by Zander Cannon, The Maxx by Sam Kieth, Locke and Key by Joe Hill, The Walking Dead by Robert Kirkman and Fables by Bill Willingham.
Does Transmetropolitan count if it was released as a comic first? I read it as three big books.
Anyway it's fantastic but also a bit hard to describe. The most I can say to draw you in is that it's a cyberpunk dystopia and the main character, Spider Jerusalem, is a Hunter S Thompson expy. He has a sonic gun that makes you shit yourself.