I'm surprised no one has answered this one for you. Adobe has a collection of information on their website found here:
Beyond that, googling sample applications, designing your own small scale interfaces (such as cataloging items in a collection via web interface), and exploring these forums is a great place to help you learn as well.
Hope that helps!
I always tell people to just read the Flex Builder 3 help system, "Flex Programming Elements" topic starting from the top and working your way down, compiling the sample applilcations and reading the text.
The help system is organized incredibly well, and you will get exposed to some great topics you just can find in any book.
If you do this you WILL learn Flex quickly.
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