It's free, but utilizes the on-board H.264 encoder built into GeForce GTX 600 and 700 Series (I think the encoder that's used to steam to their handheld PC thingy, Shield), so you'll need some fairly decent and new cards to take advantage of it. Nvidia's solution to this is ShadowPlay, a new feature of their Experience software suite that continually records the previous twenty minutes of your gaming, ready to be dumped to a file when you tell it to. It saves you from starting conversations with "That one time." and them re-enacting a game of Ricochet with condiments and plates.
The best solutions are those that will allow you to retroactively spot yourself being magnificent and then dump the previous moments. Everybody is Let's Playing nowadays (I might even do it, you unlucky people) so the new frontier of development is in making the recording and playing back of gaming moments as easy as possible.