Do You Find This Android Revolting?
Here's a chart that explains it:
In other words: This robot is cute...
And this one is horrifying.
But the Uncanny Valley isn't only caused by robots. With the advent of CGI, it's found its way into Hollywood movies as well. Here's some examples, many of which are found in the creepy new movies of Robert Zemeckis.
You wanna freak yourself out? Go check out creepygirl, an interactive website.
In the future, technology and artistry might advance to the point in which we never have to visit the Uncanny Valley again. But until then, try to avoid the almost-but-not-quite-humans.