I love The Internet Archive for its Wayback Machine, which lets you see, say, what Destructoid looked like back in 2006. But its software collection is a geeky delight, and its new Console Living Room beta is also pretty slick.
To see what games they're preserving for future generations, simply click on one of the consoles and then pick a game to try. The the magical power of web browser gaming and system emulation, everything from the Magnavox Odyssey to the ColecoVision is represented and ready to try. Not all games are listed yet, but they're working on it.
Keep in mind that this is a work in progress, so there will be no sound in the games. They say that this feature will be added soon.