Actionscript 3.0 Books

I am wanting to invest in some books to help me learn Actionscript 3.0 as well as having reference material accessible. However, I only have Flash CS3. Most of the books I see are only about Flex. There are some differences in how things are handled. I just don’t want to learn those differences so that I can then re-interpret all of the code and finally get to what I need for Flash CS3. What books would you guys recommend?