This is completely random, but I love the little gif animation above from the Pi article on Wikipedia. I've seen lots of visual explanations of Pi before... but that image above is honestly the best and clearest explanation of Pi's significance I've ever seen.
Looking at it, you immediately think, "Hey, that's weird..." and start to wonder about whether the ratios are the issue, or the decimal system, or if a circle is maybe an artificial construct (it's just a series of points, after all, in a relatively arbitrary pattern - not any more significant than a hexagon or sine wave). For example, I wonder what happens when you change the length of a single unit into Pi (i.e. Pi == 1) and see what that does to other standard calculations... well, I'm sure it's a trivial or common math exercise, but it's something I never considered until seeing that graph.
Anyways, just thought I'd share that bit of randomness for a Friday.