There are many books to learn or further Adobe Flex technology. Of all these books, I had already selected a few in previous news:

• Adobe Flex Books in French
• New Flex book in English

Today (and following the comment by Fabien), I present below a complete list of books to learn Flex 3 and ActionScript 3 in PDF format available for download.

Note that most of these books are in English, here's the list:

• Adobe LiveDocs
  • Adobe Flex 3, API COMPILER USER GUIDE
  • Adobe Flex 3, BUILDING AND DEPLOYING ADOBE FLEX 3 APPLICATIONS
  • Adobe Flex 3, CREATING AND EXTENDING ADOBE FLEX 3 COMPONENTS
  • Adobe Flex 3, ADVANCED DATA VISUALIZATION GUIDE DEVELOPER
  • Adobe Flex 3, USING ADOBE FLEX BUILDER 3
• Practical ActionScript 3 (English)
  • Full Paper
• Adobe Flex 3, ActionScript 3 Programming
• Programming Flex 3:
  • Book preview (80%)
• ActionScript 3.0 Design Patterns:
  • Complete Book on Scribd
  • Preview of approximately 80% of book
  • Chapter on the Factory Design Pattern
  • Chapter on the Command Pattern
• Adobe Air For JavaScript Developers
  • Complete book
• Apollo for Flex Developers
  • Complete book
• Other books in Google Books Preview

Finally, here is a second list of documents that may be useful to learn (AS3/Flex/Adobe Air):

• Reference ActionScript Adobe Flash Player 10 / Adobe Flex 3.2 / Adobe Air 1.5
• Data Push in Flex Using Blaze DS
• Developing and loading subapplications
• Importing Skins into Flex Builder
• Importing Flash CS3 Assets into Flex
• Testing Flex Applications with Mercury QuickTest Professional

Source: Blog de Fabien