I'd highly recommend Michelle Garcia Winner's Superflex and I'm a Social Detective books. They are written in comic book format, which my ds (not ASD, but can use some direct teaching) loves. The Superflex also has a curriculum book to go with it - really learning to think about social concepts. Browse through the other books on her site - she has VERY good resources and is often adding new ones.
Also, writing social stories to help with everyday things he might have trouble with. I assembled these into a binder and made it ds's book. He loves it. I included pictures of him in many of the stories.
Specific areas of need are important to keep in mind. I'm assuming it's not just the literal interpretations that lead you to think Asperger's, because most 7 year olds are literal, especially in reading. For this kind of stuff, though, ds likes joke books and comics. Many of the jokes have double meanings that he may or may not know already, so we can talk about why the jokes are funny - the 2 meanings they have. I bought him a Calvin and Hobbes book from Scholastic book fair. In hindsight, it's not the most appropriate book for a 6 year old, but he loves the challenge of the hard words, and it makes for some interesting conversation to talk about perspective taking, vocabulary, and humor.