I've seen:
Rain Man
Temple Grandin
My Name is Khan
Adam
Mary & Max
Mozart and the Whale
Snow Cake
I should say I didn't actually hate any of these, although I had negative reactions to Rain Man for a long time. I also saw all of these in January, so it's been several months:
I first saw Rain Man when it was new, and it made me self-conscious in ways I could not explain at the time, and I'd kind of freak out at myself whenever I caught myself doing palilalia or echolalia. I've seen it again more recently, and I found it to be better than I recalled.
I actually enjoyed Temple Grandin a lot. I loved when they'd show her literal visualizations of things mainly because I do that too, but I think the movie itself was done fairly well, whatever my personal feelings are about Dr. Grandin (not negative, I just don't agree with her on everything). I keep catching myself trying to imitate her lines at the start, but I love imitating movie lines in general, so this isn't weird. For me.
My Name is Khan was good, although people who say it seems like two different movies almost (first half, second half) do have something there. I think it works out well and has some good commentary on post-9/11 US. This film also made me realize what it looks like when I don't make eye contact, which was a bit of a surprise. It may be that the actor was exaggerating, but I don't know.
I enjoyed Adam, although I found it to be my second least favorite (Rain Man was my least favorite). I can't fully put my finger on why, although to some extent, I think it was that I didn't find much to identify with in Adam. I liked the references to real books and some of the issues Adam had with independent living (although he is much better at it than I am). I had to laugh when I saw his freezer filled with several identical TV dinners - The last time I lived on my own (well, with housemates) I think I managed to eat four different meals over the course of the month.
Mary & Max was really good - surprisingly so, for me. The ending was well done.
Mozart & The Whale was unique in all these movies in that it showed several AS individuals. Also interesting in that it's based on a true story. Anyway, when I saw it I felt as if the characters' autistic traits were exaggerated, although I'm not sure how I feel about that now.
I liked Snow Cake, although I felt like in some ways Linda was kind of peripheral and central to the story at the same time. I do relate to her reactions whenever her space was invaded (like the kitchen being hers, chasing everyone out of the house).
I guess the two I really liked the most are Mary & Max and My Name is Khan. It's hard for me to judge which one is the best portrayal of autism or AS because I only really have myself to compare them to, and I am not necessarily (as far as I can tell) like any of the characters in the films, portrayed as they are by NTs and sometimes coming across almost like composites of two or more autistic people (does that make sense to anyone else?). I guess my third is Mozart & the Whale, but I really really want to read the book.