Please try not to mention Penny Arcade herein, alright?
The ongoing history of the Achewood plushies and their friends, through insanity, financial enterprise, love, gruesome murders, trips to foreign countries, outer space and the great beyond. Embedded into story arcs, the strip is much more fun to read in a sequence of strips, but you don't have to. Chris Onstead makes up for any loss of plotline with pretty much everything such a simplistic webcomic can offer for amusement in a few panel's worth of time. Of course it doesn't stop there or anywhere. The characters even have their very own weblogs!
http://please.leisuretown.us/leisuretown/
Always worth a revisit into these golden times when the strip was still created: An LSD trip of a weirdo with tourette syndrome.
Pretty much the best crappy and trashy MSPAINT-style comic strip out there.
Doesn't get updated lately, unfortunately. PS: MSPAINT rules!
http://www.elftor.com/elftor.php?number=112
Cat and Girl involved in & about philosophy, economics, politics, literature, art theory & practice and a lot more stuff, like carefully acted out studies of the effects and consequences about the consume of paint and a few remarks on the illustrous zombie Joseph Beuys.
Submitted dreams forced in and acted out on the format of 4 panels per strip.
The results are pretty worthwhile.
http://www.helsinki.fi/~voinonen/vibbelandia/
Not really a webcomic but a nice selection of art by this Finnish artist with a collection of his own comic strips, some of them translated into English.