One I missed before was Sesame Street- there is an autistic muppet called Julia. She seems to have gotten a bit of a mixed response from the Autistic community. Some were upset that they didn't get an autistic actor to voice the character or an autistic writer to work on her scenes. From the little I've seen of her appearances I quite liked her. In particular, I liked one part where one of the adults said to Big Bird "Julia has autism." Big Bird asked what that meant and the adult responded "well, for her it means..." I thought it was cool that they were showing that not all autistic people were the same.
While they've never actually said on the show that she was autistic, the character, Bones (aka Temperence Brennan) on the Show Bones always struck me as behaving like someone on the autistic spectrum and apparently I'm not alone in thinking that. It's a pretty positive portrayal, as was the one on Waterloo Road, and challenges the assumption a lot of people still have that autism only affects boys and men.