Here is a movie list first generated on Autism Speaks. I've added a few of my own.
(I listed Netflix first because there is no fee. When I couldn't find a movie on Netflix, I looked on Amazon Prime for those who have that membership. Lastly, I looked to Amazon streaming rentals and Amazon DVDs that are available for a fee.)
A Mother's Courage- Netflix
Adam- Amazon streaming rental
Best Kept Secret- Netflix
Black Balloon- Amazon streaming rental
Dad’s in Heaven with Nixon- Netflix
Fly Away- Netflix
Loving Lampposts - Amazon streaming rental
Mary and Max- Netflix
Miracle Run- (LifeTime movie- available on DVD from Amazon)
Mozart and the Whale- Amazon streaming rental
My Name is Khan- Amazon streaming rental
Ocean Heaven- Netflix
Rainman- Amazon streaming rental
Sounding the Alarm- Netflix
Snow Cake ? This was listed in comments as a favorite but I couldn't find where it is available.
Temple Grandin- Amazon Prime
The Story of Luke- Netflix
The United States of Autism- Netflix
What's Eating Gilbert Grape- Netflix
Note: I have seen several of these movies, but not all. Let me know what you think of the ones you watch.