Abobe's Flex documentation

A lot of Flex documentation is available within the Flex IDE and online through Flex3 Livedocs. However, sometimes its nice to have the information in book format, and Adobe makes all of its online info available as PDFs from its Adobe Flex resources page. All are useful, and the price is right (free). Some must-haves:

• Flex 3 Developer Guide - 100's of pages of clearly written info and examples. Trust me, you'll access this one constantly in the beginning.
• Programming ActionScript 3.0 - Excellent language reference for AS3 newbies. Also with many useful examples.
• Creating and Extending Adobe Flex 3 Components - A guide to creating custom classes, both MXML and AS. Chapter 9 is especially good, with emphasis on the Flex component lifecycle (which you must understand to create optimized AS3 classes).

Some good Flex3 books

I can personally vouch for the following books:

• Flex 3 Cookbook by Todd Anderson, Joshua Noble
• ActionScript 3.0 Cookbook by Joey Lott, Keith Peters, Darron Schall
• Essential ActionScript 3.0 by Colin Moock
• Adobe Flex3 Bible by David Gassner
• ActionScript 3.0 Bible by Roger Braunstein, Mims H. Wright, and Joshua Noble
• Advanced ActionScript 3 with Design Patterns by Joey Lott and Danny Patterson
• Professional Adobe Flex 3 by Joseph Balderson, Peter Ent, Jun Heider, Todd Prekaski, Tom Sugden, Andrew Trice, David Hassoun, Joe Berkovitz
• Advanced Flex3 by Shashank Tiwari, Jack Herrington, Elad Elrom, and Joshua Mostafa
• Enterprise Development with Flex by Yakov Fain, Victor Rasputnis, Anatole Tartakovsky
• Foundation Flex for Developers: Data-Driven Applications with PHP, ASP.NET, ColdFusion, and LCDS by Koen De Weggheleire, Sas Jacobs

The first three books are published by O'Reilly, the premier site for developer resources. Like most O'Reilly books the three listed above are very thorough and clearly written (I especially recommend anything written by Colin Moock).

The Flex3 Bible is written by David Gassner, an instructor for the Lynda Flex3 online training videos (I also recommend these Lynda courses). A good starter book, it takes you from the basics up through the important classes (with good basic examples) and on to a large section on Flex integration with various data source/standards (SOAP, a lot on Adobe's ColdFusion and BlazeDS, some on ASP.NET and PHP).

The ActionScript 3.0 Bible is a book for beginners to advanced Flex/AS developers, a great reference with a wealth of useful info (tho, as the title implies, it's more focused on AS than MXML).

Advanced ActionScript 3 with Design Patterns is, as the title suggests, for more seasoned programmers. If you haven't yet learned design patterns and want to learn using ActionScript code for the examples this is a great book for you (actually, if you're familiar with design patterns but new to AS it's also useful). Note that the co-author is Joey Lott, the instructor for the Lynda AS courses. by Joey Lott.

Professional Flex 3 is a monster at 1400+ pages, it lists for $50 but is worth every penny for a newbie or novice - not just comprehensive but clearly written by a team of eight topnotch Flex developers.

As for Advanced Flex3, I highly recommend this once you're comfortable with Flex/AS3 basics. It has a nice overview of Design Patterns and lots of info on architecture issues. All in all, it's really well written (especially the chapters by Tiwari) and full of advanced topics/tips/traps.

Enterprise Development with Flex is new (Spring 2010) and I've just started diving into it. It's for more advanced Flex/AS developers, giving a broad sweep of knowledge required for creating industrial-strength Flex apps. Its broader and more advanced perspective is unlike the other books listed here with the exception of Advanced Flex3.

Flex for Developers is notable for its large section on various data access methods including ColdFusion, ASP.NET, PHP, and LCDS (I will say that the title's usage of "data-driven applications" is a bit misleading, the provided case studies aren't apps whose execution is configured/customized through metadata, they're simply really good working examples (primarily of data access methods).