I'm a late comer to Randall Munroe's xkcd.
Wikipedia tells me the web comic will be five years old next September.
I'm sorry I've missed out, but both the Achive or the feed are helping me catch up. The loving Wikipedia article includes many annotated comic citations.
Munroe is a genius. He must also be a rebel, for it's not at all clear how he makes any money. He reportedly donated all the proceeds from his one book, and there are no ads on the immensely popular web site.