So! Let's get started.
Sinfest. What can I even say about Sinfest? This is where it begins:
It just gets better from there. Slick (the Calvinesque fellow about to strike the Faustian bargain) and 'Nique (the Hobbesian hottie with whom he is perpetually stuck in the friendzone) are the stars of this daily webcomic with a 4000+ strip archive. Read the whole thing if you have time--the artwork improves, the many characters and their relationships develop and change, and the strip slides along the spectrum between 1-offs and longer, more focused story arcs--such as when the devil, realizing he's just playing the role God assigned him, commits the ultimate act of rebellion by walking away from his booth and hitting the beach.
Then there's God himself, who speaks to man through
It's incredibly creative, endlessly entertaining, beautiful to look at (at one point, the Sunday strips began appearing in full color) and hits altogether too close to home in discussions of politics, pornography, theodicy, relationships, loneliness, pot, and pets. It also gave us what may the greatest line of any webcomic ever, in panel 2:
I leave you with some of my favorites: