Sick of hearing that Einstein's famous equation E=mc^2 is part of Special Relativity without further explanation? How often have you actually had to say it yourself not quite grasping how it follows from the simple postulates of Special Relativity?
Well I just could not take it anymore and after browsing through large numbers of sources who keep just stating without explaining, I finally found this website, which does a great job in really tackling the problem and putting the famous equation into its real context within Special Relativity.
I am not saying that when talking to non-specuialists one needs to go through the mathematical derivation of the equation, but at least knowing where this derivation starts and ends will give you, and your audience, a real feel of where the equation stands.
Sufficient to be able to know and tell that it comes from applying the concept of the speed of light being the maximum speed achievable, to the Kinetic Energy. Just as applying it to other aspects of motion gives you time dilation, space contraction and mass increase at high speeds, the other three consequences of Special Realtivity. Simple as that.
So, well done, anonymous author of this website. For all the rest: See? It wasn't that hard!