This sight offers a great deal of information.
One of the tools I really like is the video clips they have put together demonstrating some of the early warning signs for autism. There are instances where you can see two clips running side-by-side, one showing a child with an autistic spectrum disorder, and the other a child without, performing the same requested tasks. The differences in their reactions can be subtle, but if you watch a few, you can begin to see the patterns. I think when you are first confronted with the possibility of autism, especially for very young children, it seems difficult to believe that watching your child play with plastic cups, or a windup toy, can really give the docs insight into your little one, so this helps to explain how. You'll find these demonstrations under "Video Glossary".
Just thought it might be useful for someone.
Autism Speaks, Home Page