Todd Yard: Foundation ActionScript 3.0 Image Effects
One of the first books I've seen to cover the new 2.5D features of Flash Player 10.
Todd Perkins: Search Engine Optimization for Flash
Good SEO tips. (I wrote the foreword for this one.)
Alaric Cole: Learning Flex 3: Getting up to Speed with Rich Internet Apps
Juan Sanchez: Creating Visual Experiences with Flex 3.0 (Developer's Library)
Marco Casario: Flex Solutions: Essential Techniques for Flex 2 and 3 Developers (Solutions)
Rich Shupe: Learning ActionScript 3.0: The Non-Programmer's Guide to ActionScript 3 (Learning)
Gary Rosenzweig: ActionScript 3.0 Game Programming University
Colin Moock: Essential ActionScript 3.0
This book is, well, essential.