Tan Le: A headset that reads your brainwaves - TED Talk (youtube.com)

I was quite amazed that this is actually a purchasable product. http://www.emotiv.com/ has development kits for sale worldwide, and a consumer headset available for US customers. This seems a far more interesting way to spend $500 than on an iPad.

Currently window only, but apparently linux support is in the works as well.