I would start from here:
http://www.actionscript.org/resources/authors/364/Bryan-Grezeszak
Since you're an experienced as2 developer you can go with this book: http://www.amazon.com/ActionScript-3-0-Design-Patterns-Programming/dp/0596528469/
Also I always keep Colin Moock's Essential AS3 under my hand: http://www.amazon.com/Essential-ActionScript-3-0-Colin-Moock/dp/0596526946