Speed Demos Archive puts on some great livestreams of speedruns, as I came to realize far too late into the last marathon. I'm heading into the latest event, Summer Games Done Quick 2013, bright and early -- you should join me! It's for a good cause, too: the five-day stream is raising money for Doctors Without Borders, a very worthy organization.
Beyond playing through a bunch of different games ranging from absolute classics to more modern favorites in ways that will have you rethinking everything you know and love, there's often quality commentary to keep you in the loop on whatever insanity is happening on-screen. If you've ever wondered how some of us could possibly enjoy watching other folks play games, speedruns might be the missing link for you. The full schedule can be found over here.