I love webcomics. Around the middle of high school, there was a point where I was reading over 200 regularly. I was also listening to a podcast about them, called Digital Strips. (Which I think I'll check out again soon.) As the years have passed since, for one reason or another the number of comics I read significantly dipped -- switching computers a lot took out a pretty huge chunk, because I could never figure out a smooth way of transferring my hundreds of bookmarks.
Some of my favorite comics just ended, like Comedity and MacHall. Some got overwhelming, and I couldn't manage to get caught back up between periods of not reading, because I didn't have a computer or lost my bookmarks. Really great comics, like Megatokyo and Dominic Deegan, too -- I hope to get back to them some time.
This comic belongs by far at the top of my list. I'm not sure it's my favorite (I'm not good at picking favorites) but it's easily the comic I most eagerly look forward to.
There tend to be big waits between page releases, but it's worth it. The artist, Aaron Diaz, puts an incredible amount of work into drawing the pages, and it shows. I would hang his comics on my walls[1. if I weren't broke.].
As far as the plot, it's excellent. Cryptic, science-flavored, and beautiful walls of text. Seriously, the pages may only come out like twice a month, but each one will hold you over. Read it five or six times.
He also maintains a tumblr, the only one I followed before I really got into tumblr last month, called Indistinguishable From Magic. He writes about sci fi, comics, art, his process, and is just generally awesome all over the place.
It's a lazy comparison to say that this story is like Harry Potter, but it's a place to start. It's mystical and mythical, and takes place in a mysterious boarding school -- although, as the plot goes on, it's less and less clear whether being a boarding school is even on the radar of priority among the people in charge[2. if there is anyone in charge what if it's just machines or maybe it's some elder deity oh god it's all so mysterious].
The only other substantial parallel I can make to Harry Potter is that the maturity of the content ages with the characters, which is a pacing style I admire, and might imitate if I ever write a children's series.
The art is gorgeous. It started out at the level of well-drawn picture books, and has only gotten better. A well-chosen page might look good hung on a wall.
This is my favorite regular funny comic. I mean, xkcd is great and all, but where it leans towards jokes about math and coding (though definitely covering a wide and compelling spectrum,) SMBC leans towards philosophy and literature (though definitely covering a wide and compelling spectrum,) so the jokes tend to hit home with me a bit more. I've shared several strips with my philosophy teacher, and I find I'm frequently surprised with how depressing she finds their conclusions.
Zach Weiner[3. lol], the writer and artist, has plenty of other projects going on as well -- the currently off-season
SMBC Theater, a YouTube sketch series; The Weinerworks, Zach's personal blog; and The Weekly Weinersmith, a science podcast he records with his wife, Kelly Weinersmith[4. lol]. He, along with co-creator James Ashby, also raised the money via Kickstarter to create a season of their own comedy space opera. I'm looking forward to that. [EDIT: there was a formatting error in this paragraph. I fixed it, at the cost of an unnecessary paragraph break. 6/13/2012]
There's not much to say about xkcd that hasn't been said already. Randall Munroe is arguably the king of nerd comics on the internet. I remember when I discovered xkcd in high school, and found out that a lot of my friends were actually not very funny, and had just found xkcd before me and not cited their jokes.
If I had to pick a favorite comic, Questionable Content would have a good chance of winning. It's definitely the comic I've got the most emotional investment in. The art style progresses through the years from 'eh' to awesome, and there are occasionally pretty posterworthy strips. Also, the t-shirts are pretty much always great, and it comes out 5 days a week.
As it's gone on, the writer, Jeph Jacques, has gotten better at pacing and storytelling, but even if the first 500 strips are kind of easy to make fun of for the slow progression of relationships, they're not really bad. It was more the kind of agonizing withholding of catharsis that you get with the romantic subplots in sitcoms.
And the casual weirdness of the setting is amazing. I love it so much. AnthroPCs are the best world-feature evar.
El Goonish Shive is one of my favorites -- it's one of the comics I've consistently come back to for years. Still, I sometimes feel weird about recommending it, mostly because it took a long time to get on its feet. The early strips, for a kind of a long time, are just not very good, both in art and in plot. To be fair, the setting, world building and dialogue are pretty solid from pretty early on.
But if you get through it this comic is great. It unfolds at a very slow pace -- the writer, Dan Shive, has said that he writes more for the archives than for the daily reader -- but that just means that once you find that point where you're into it, there's going to be a huge pile of great comic to read. And once you get to the present, it's not too bad. Stuff still happens every strip, it's not like watching Dragon Ball Z.[6. Q. How many DBZ characters does it take to screw in a lightbulb? A. One, but it takes six episodes. (I can't remember where I heard that joke.)]
Honorable mention: Homestuck
This is the comic I'm currently reading, and if it weren't so painfully difficult to catch up I would have started much earlier. MS Paint Adventures comics seem so far to be always awesome. But they're also always super-difficult to catch up on.
I had actually caught up on Problem Sleuth just as Homestuck was starting. I'm still sort of kicking myself for not just reading it then.
Well, that ended up being a lot longer than I'd planned. (When I started, it was a short commentary on Gunnerkrigg Court.) I hope you enjoyed it, and I hope you want to check out some or all of these comics.