Styles explorer Allows you to experiment with properties of a host of Flex components. Very important!
Flex Components Absolute must site for all Flex coders: Tour de Flex
switchonthecode Excellent Flex files with detailed explanations
Chafic Kazoun & Joey Lott. Programming Flex 3: The Comprehensive Guide to Creating Rich Internet Applications with Adobe Flex.
A view of the future with Adobe MAX
Challenge: Create a new file in Flex and place a TabNavigator (or any other component) on the stage. Now rewrite the file using only ActionScript (i.e. ActionScript classes) to create the functionality of the component. This is a tricky but extremely valuable task that will teach you about working with classes, display objects, and style sheets..