What Non-Flex Resources Have Helped You with Flex?

In a discussion with some Adobe Community Experts it came up that we expect you to have a reasonable amount of prerequisite knowledge to use Flex. You are better off if you have some familiarity with web development already, especially in areas such as exposing data as services, OO programming, CSS syntax, XML, etc. But not everyone who decides to learn Flex has all of that experience. So we were thinking it could be good to build up a list of general resources that can help with all the things you probably ought to know to improve your chances of success with Flex.

I don’t know where we’ll put this, but please start by commenting here on suggestions you might have for books, blogs, websites, online tutorials, etc. that provide the background material you might need to write any RIA, not just a Flex RIA. Feel free to be very specific, chapters in a book if you know them for example.