Forrest is just slow. He's very naive, but i think that has more to do with his relatively low intellectual abilities than being on the autistic spectrum.. He doesn't show any autistic-like behaviors at all, really. Bubba's shrimp obsession could definitely be some kind of autistic thing, though. I don't think Ross is Aspie in any way. He's really into paleontology, but he still manages to have a wide range of interests outside of it.. and he has tons of friends. Good friends, too. He also finds a lot of dates. He's just a bit of a nerd at times, but still very socially functional. Monica might have Obsessive Compulsive Personality Disorder, maybe?
I still think sheldon is the closest to being aspie of any popular tv show character. He even comes out and says a few times that he doesn't recognize facial expressions, and he's very inflexible. He has his group of friends, but if you've seen all the episodes the only reason he even has then is because he needed a roomate, Leonard ending up being that roomate, and Leonard's friends just started hanging around with him because they were Leonard's friends and he lived with him. And, even with them his reciprocal communication isn't great, he always goes into monologues despite everyone else being annoyed, he rarely picks up sarcasm, and he generally only talks about what he wants to talk about. The only really un-aspie things about him are that he has really good eye contact and has a wide variety of interests.