Let's Play videos are rather popular these days, and Nvidia is introducing ShadowPlay to make it easier for PC gamers to capture their finest moments. It's a new feature of their Experience software suite, and it continually records the last twenty minutes of your gameplay.
Although it's free, you'll need a fairly recent card to use it; it utilises the on-board H.264 encoder built into GeForce GTX 600 and 700 Series. Apparently you can get 1920x1080, running at 60 frames per second, if you're willing to put up with an enormous file size.
ShadowPlay can also be used for live recording too, for if you know in advance that something incredible is going to happen. It'll be available from October 28.
Thanks, Rock Paper Shotgun.