I am sorry I cannot give you any definitive answer on this as I have not read any books yet on Actionscript 3. However, what I CAN tell you is that I learned actionscript 1 through books written by Robert Reinherdt and Joey Lott. These were the "Flash <topic here> BIBLE" series (beware...others have similar names not by these authors). I look for these authors now as their books are excellent. I hope this is of some help to you. Check out Amazon for books by them. Good luck.
http://www.cartoonsmart.com/actionscript3_index.html they're not books, they're video tutorials. The best ones too.
The best is CartoonSmart http://www.CartoonSmart.com I've purchased almost every tutorial that Justin has made. He's great at what he does! If you want to get a good start with the basicas try out Lynda.com : http://movielibrary.lynda.com/html/modListing.asp?sid=81 Another pretty good spot for video tut's is gotoAndLearn: http://www.gotoandlearn.com/ And a couple more: http://www.entheosweb.com/Flash/default.asp http://www.cbtcafe.com/flash/actionscript.html http://library.creativecow.net/video-tutorials/adobeflash