Two good American comic artists, who both happened to live just down the street from my place in Berkeley, CA a while back, are Adrian Tomine (Optic Nerve) and Daniel Clowes (Ghost World, Art School Confiential). They're somewhat similar in that their stories usually focus on young characters in urban settings dealing with every day life and relationships. Like the somewhat autobiographical character in Art School Confidential, Clowes is a bit on the nerdy side.
http://lambiek.net/artists/t/tomine_a.htm

Preview of a Tomine story: http://www.drawnandquarterly.com/imagesPreview/a462fba9cc8e66.pdf

Tomine is published by Drawn and Quarterly, a great Montreal-based graphic novels editor, which has a great lineup of artists. that lineup itself is nicely produced in a series of small self-portraits on their featured artists page:
http://www.drawnandquarterly.com/artHome.php

You can't have a thread on modern comics without mentioning Robert Crumb, an eccentric artist who was a big part of the late 60s counterculture and was very influential in "blowing up" the genre. http://www.rcrumb.net/

This famous poster of his, titled Short History of America, was presented frame-by-frame in a recent major conference on sustainable urbanism, it was a huge hit and really underscored some of the basic ills of modern land developement:
http://www.crumbproducts.com/prints_images/sha.gif


There are some definite Crumb influences in Joe Sacco's approach. His most famous books, "Palestine" and "Safe Area Gora˛de" won the American Book Award and Eisner Award. "Palestine" is a remarkable book, as poignant a read as "Maus". The review that comes up on top of the Amazon customer reviews is remarkably spot-on:
http://www.amazon.com/Palestine-Joe-Sacco/dp/156097432X