The new Nintendo 3DS is able to produce a 3D image without the need for glasses. How can it do this? By using a "parallax barrier". Here's what one looks like up close.
A parallax barrier is basically a "screen" on top of a regular screen, which has tiny little blocks in it that allow only part of an image to be seen by each eye. By displaying two separate images for each eye, the barrier is able to trick your brain into thinking it's seeing an actual three-dimensional object.
Nikkei tore a 3DS to pieces over the weekend, and provided these up-close shots of the screen in action. In the first image, with the dark stripes running down the screen, you can clearly see the "barrier" in action. On the second image, though, you can see what the LCD screen looks like with the 3DS' "3D Slider" turned all the way down.
While the barrier is still visible if you stare real hard at the screen, for regular gameplay it would no longer be capable of displaying a 3D image.