Robert Penner's Book
Book reviews aren't something I normally do, but Penner's book, (Programming Macromedia Flash MX), is the best book on FlashMX I've seen so far. UltraShock set up a forum for it: interesting discussions, and Penner himself is participating.
Along with Moock's book, due to be released on Dec 19th, Penner's book may guide actionscripting to a new level of maturity.