What are your favorite webcomics?
As someone working in science, I’m particularly fond of XKCD and PHD Comics.
XKCD:
And for everyone who has done a PhD or a postdoc PHD Comics is always dead on:
A few of my favorites, although I haven’t really followed them closely in years.
I do enjoy PHD… even though over half of the jokes don’t work for the humanities at all. But I still enjoy them. 
It’s time that we give ourselves a cool recursive acronym: GWC, which stands for Gwc Water Cooler.
Wow, so many great recommendations, thank you
Isn’t the forum already the GWC Water Cooler?
I also love Garfield Without Garfield which just might be one of the greatest idea ever: what if Garfield was only a Head Garfield?
A new pretty funny webcomic: Superuseless Superpowers. All you wanted to know about the most useless superpowers, such as in-flight flight:
LICD is the bomb! I’ve been a faithful reader since somewhere in the first year… Absolutely wonderful humor, even if it’s a little umm… crude and sexist? :o
Aside from XKCD (which, really, is required to maintain a platinum geek card) I read “Order of the Stick” and “Erfworld” (not our Erf.)
OotS is based on D&D, and Erfworld is based on fantasy minatures. Erfworld requires the least familiarity to get the majority of its humor (e.g., you can’t swear in Erfworld.) Both are at Giants In The Playground.
I’m also fond of Penny Arcade and Achewood, although I read them in fits and starts.
G-G is great. My favorite: 
The only other web comic I read with true regularity (other than the requisite xkcd, of course) is Kate Beaton (for history dorks)
Thought I would revive this thread and post some comics I had been reading lately.
Ctrl-Alt-Del
Comic about gaming and gamers - mostly.
Legostar Galactica Technically, not a comic, but done in LEGOs. Parody of Star Trek, Star Wars, B5, and most other sci-fi series. (Oddly, not so much BSG). Updates everyday and has been going for over 5 years!
Concerned* Parody based on the game Half-Life 2. Follows the adventures of Gordon Froman, (not Freeman) in City 17. No longer being published, but a great read if you have played the game.
*Also technically not a comic, but machinima.
I was going to bring up XKCD and PHD…but you guys beat me to it 
I feel ya there. I’m in the same boat.
I also really like Amazing Superpowers, Hark, A Vagrent, and although not really a web comic, Survivng the World is a great site as well.
Keep in mind, Vagrant is a bit of an acquired taste…particularly if you are a lover of history.
Here’s my list, not surprisingly there are some repeats 
A couple of my favorites have wrapped up their storylines, but in some ways that’s nice if you’re starting from scratch and just want a good read.
Sinfest
Least I Could Do and Looking for Group
Questionable Content
Wapsi Square
Dr. McNinja
Order of Tales (ongoing) and Rice Boy (completed)
Nothing Better
Hark, A Vagrant
Ugly Hill (completed)
Kukuburi (careful, updating is spotty and it’s easy to get hooked)
The Port (also spotty on updates, but awesome!)
I also loooooved Kiskaloo, but the creator Chris Sanders (Lilo & Stitch) has not updated it in more than a year, presumably because he has other nice jobs to keep him occupied.