XKCD

I have been looking through old XKCD comics, and after many hours research have decided that this is probably the best one:

http://xkcd.com/496/

A few other brilliant ones to brighten up the day:

http://xkcd.com/182/

http://xkcd.com/327/

http://xkcd.com/227/

http://xkcd.com/466/