xkcd is such a classic webcomic series, I assume that everyone knows of it (and it's not the first time I've referred to it). After all, it has been the answer to a question on 'University Challenge'. A little thought tells me that this can't be so - hence this post.
It's a superbly simple strip that bills itself a 'webcomic of romance, sarcasm, math and language'. Add in 'science' and 'computing' and you've a superb description (though it doesn't flow as well). The strip is never going to be to everybody's taste, and you need quite the range of geeky background knowledge to get all of the strips (if I tell you how many I get, it won't reflect well on me, either I'll look ignorant or boastful).
The strip is simply drawn, but it's the idea of the strip that matters.
Sometimes the strip will just have a social truth:
Sometimes it will make a point about science:
... or just proffer a handy tip.
Each strip is different and unexpected, each is clever, each unabashedly geeky. It's necessary reading.