xkcd is smart and fun; nerdy but in a way that is somehow still cool.
Maybe more than any other comic, I’ve seen these used in ~presentations to get a point across in a lighthearted way, and I even have a friend who has an epic xkcd infographic mounted in their office.
As a bonus, the website is set up to allow easy browsing for a quick pick-me-up (pro-tip: there is typically hovertext on each comic).