Start here: [url=http://macscripter.net/books/]http://macscripter.net/books/[/url]
The most recent books are probably: Sams Teach Yourself AppleScript in 24 Hours by Jesse Feiler; AppleScript 1-2-3 by Sal Soghoian. And AppleScript: The Definitive Guide by MattÃ? Neuburg from O’Reilly.