I read a lot. Like 29 regularly read ones and about 10 other less frequently read ones.
Basically the top ones that I read (and haven't already been mentioned) are:
Order of the stick- Simple comic that pokes fun at D&D. Currently at 863 comics and a bunch of fun. Updates about once every week or two, but recently the artist injured his hand so it hasn't updated for a little while well he recovers.
El Goonish Shive - A funny comic about a group of high-school age kids and their various transformative shenanigans. Has a few more serious moments, but mostly runs on funny. Updates MWF.
Girl Genius - In a world of mad scientists called "sparks" our main heroine is the craziest of them all. Basically the founder of the
Gaslamp Fantasy Genre (Warning: TvTropes!).
Dominic Deegan - It started as a gag-a-day strip about a seer but got a fair bit more serious as it went along. It still descends into puns every now and then though. Currently updates MTWTF, but is getting into the final chapters of the comic.
Dan and Mab's Furry Adventures - A fairly funny webcomic that relies on a combination of gags and character development. Currently updates MWF but has a tendency to upload without shading and then shade later. Has a large amount of art development from beginning to end.
NerfNow! - A gaming comic that relies on one-shot gags. Updates every few days with a new comic. Can be a little fanservice heavy at times, but never actually shows anything.
Exterminatus Now - A hilarious comic that is what you get when you mix Sonic the Hedgehog, Warhammer 40K, and a bunch of black comedy. Updates once a week usually and contains some language and blood.
Yosh! Saga - A comic about a bumbling artist (who is invincible to everything) in a world that magic has been unleashed on. Has a fair amount of robot girls as well. Alternates between character development, jokes, and more serious stuff. Updates MWF.
Gunnerkrigg Court - A comic about a girl going to school in a world divided, one side driven by technology and the other by magic. Updates MWF and is powered by character development.
MegaTokyo - A comic about two friends who go to Tokyo and get stuck there due to spending all of their money. Runs on character development but due to the fact that Tokyo is two worlds overlaid on each other (one of magical girls, zombies, and other anime things with the other being realistic) can have some hilarious moments at times. Updates infrequently, but as it has 1348 comics if you pace yourself you could probably stretch it out a fair bit.
Sequential Art - A comic about a artist with large eyebrows, his various friends, and the various misadventures that happen. Fairly funny at times and updates often (artist runs two webcomics and does a MWF between the two of them).
Jack - A webcomic about a world where Furries have since replaced humans. The title character has become the grim reaper and the majority of the comic takes place in hell. A
very deep comic, but contains
large amounts of adult content (language, blood, gore, nudity and various combinations thereof, don't even try to read this at work).
Housepets! - A webcomic in a world where pets can talk and the various misadventures they get into. There is some more story-arc driven stuff, but it's mostly behind the scenes. Updates MWF.
Grim Tales and
PowerPuff Girls Doujinshi - Amazing comics. The author has basically taken all of your favorite cartoons as a kid (Grim Adventures, PPG, Dexter's Lab, Samurai Jack) and thrown them together with a few original ones. Amazing art styles and very fun to read. Specifically Grim Tales deals with the future son and daughter(who has a brother complex) of Grim and Mandy from Grim Adventures and PPG Doujinshi deals with everyone when they were kids.
Those are pretty much the top of what I read, minus what other people have listed before (namely Schlock Mercenary, Least I Could Do, Looking for Group, Unsounded, xkcd, and Dresden Codak).