Back in the day when I had time to regularly keep up with web comics, the two I would frequent were Homestar Runner (in particular Strong Bad Emails) and Foamy The Squirrel. Check them out at the links below.
Foamy the Squirrel - http://www.illwillpress.com/
Homestar Runner - http://www.homestarrunner.com/main11.html
What are some of your favorite web comics?