Claymation for adults. No, I'm not kidding. And it's very good. It lacks an MPAA rating, but it would be pretty rough for kids, I think.
Mary Daisy Dinkle is 8 years old, living in a bleak Australian suburb with two barely-functioning parents, and a pet rooster. She has "eyes the color of muddy puddles and a birthmark the color of poo." There's a neighbor confined to a wheelchair (because he's legless) and his house (because he's agoraphobic, which Mary pronounces "homophobic".) Mary's shunned at school, and profoundly lonely.
Max Jerry Horowitz, on the other hand, is an obese Jewish New Yorker with severe Asperger syndrome. He has no friends other than the imaginary Mr. Ravioli who sits in the corner, reading self-help books. His neighbor, Mrs. Bevan, is near-totally blind, bald, and a terror—literally—in the kitchen. Max has a fish, or rather a succession of fish, named "Henry" whose life expectancy is short.
One desperate day, Mary picks Max's name at random from a New York phonebook, and sends him a letter. This starts a rocky relationship that persists for years.
The movie is unique, carried by striking visuals, an immensely creative script, and great voice talent. (I especially enjoyed Philip Seymour Hoffman as the voice of Max.) It's very darkly humorous, and racks up an impressive body count by the end. (For example.)
I don't usually point to promotional websites, but this one is very well done.
The genius behind it all is writer/director Adam Elliot. The DVD contains his short movie Harvie Krumpet which won the Oscar in 2004 for Best Animated Short; it covers similar territory.