There's a thread
here, but it's quite a ways down. I'll post an updated version of what I posted in that thread since my list hasn't changed much.
Sluggy FreelancePenny Arcade: Not bad, but when it's funny, it's really funny.
User FriendlyBlank It: I highly recommend. While most web comics are episodal, this one is one long storyline arcing over the whole series, sort of like Lost.
Ctl Alt DelCtl Alt Del Sillies: Not updated frequently.
Joe and Monkey: This one's been discontinued, but it was good.
Least I Could Do: One of my other favourites, tons of 80s pop culture references (but for some reason Looking For Group never caught my fancy...).
Everyday Decay: Frequently misses his schedule, but otherwise not bad.
The Zombie Hunters: This one is okay, but if you want a zombie comic, try Everyday Decay. The Zombie Hunters is rather slow (it takes literally months to progress the plot sometimes; it's been stuck in a flashback for so long, I'm wondering if the stuff before it was actually a flashforward instead), and kind of mediocre. Art's great, though.
Roomies/It's Walky/Joyce and WalkyShortpacked: Even more 80s pop culture references. From the same guy that does the Walky/Roomies ones.
Lil Formers: I'm probably going on a limb here, but this one is rarely if ever funny. Don't know why I really read it anymore, but I do....
Rob and ElliotHero Squared: Quite funny. More of a published superhero comic (ala Marvel or DC) than a web comic.
Out There: More a "domestic" comic (for lack of a better term), but not bad. Not awesome, but not bad.
Real Life Comics: One of the earliest web series, but I have to say not terribly funny. Don't know why I read it, but I do. It's got a couple of funny ones, but otherwise it's very typical.
The Book of Biff: One of my other favourites.
My New Filing Technique Is Unstoppable: Another really funny one if you're into maligned clip art.