Oooh, so many good ones...
I see Knight Run hasn't been mentioned yet. It's like Starship Troopers, Mass Effect, Halo, and Star Wars, all wrapped up in a nifty action space opera. It's tragic though, and has a really good (bitter sweet) ending. Lots of Harsher In Hindsight.
Dresden Codak is a western webcomic with inconsistent, lengthy updates, but the art is really nice to look at. Offers plenty of whimsical humor regarding science and transhumanist philosophy.
A Fairytale for the Demon Lord provides an interesting well-drawn story of a knight and the princess he looks after. Has one of the coolest loop twists I've ever encountered. Lots of Odin.
Deadman Wonderland is a manga about a male middle schooler framed for the murder of his entire class and sent to the titular prison built like a theme park. I'm not good at summarizing things, but it's a well done tragic tale, where Break The Cutie occurs again and again. Series is almost done.
Gone with the Blast Wave is another western webcomic, this one is a post-apocalyptic humorous tale of two infantrymen (a sniper and pyro) lost in a bombed out city. It's a three way fight between the Red, Blue, and Yellow factions. Very deadpan humor. The comic itself used to be dead, but is now back to a consistent (monthly) release schedule.
Franken Fran. Another manga, this one is what I'd imagine would compose a med student's nightmares. It's very, very dark humor, with lots of tragic irony. Pretty much follows the exploits of a frankenstein-like surgeon, who will keep you alive at any cost, whether you want it or not. Completed series.
One-Punch Man. A manga that pokes fun at all the superhero cliches. Follows the life of Saitama, a guy who can insta-kill any threat with a single punch, which frustrates him to no end, and yet he gets no recognition for his acts of heroism.
Drifters. If you loved Hellsing, you'd love this, probably more. Basically, famous people from history, thrown into an alternate realm where they must fight to conquer save the mystical/fantastical inhabitants currently being oppressed. Cool stuff.
Edited by Paper, 12 May 2014 - 07:34 AM.