If you have Flex Builder 3 installed, or even just the SDK, you can build the Adobe Flex 3 Component Explorer on your machine and play around.
Build the SWF files, then create a new project in Flex Builder and you're good to go.
Note: you can also build the Japanese version of the explorer (although I did not try it).
1) Open a DOS window and CD here:
C:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0\samples\explorer
2) Execute build.bat or build.sh on Mac (I've only tried windows, so no guarantees there.
3) Open Flex Builder and create a new project, pointing to the above directory. Make sure you indicate no folder for the "Main source folder" (delete src).
4) Build, launch, play around and you're ready to learn a lot!
Note: you'll need to copy the following folders to the bin-debug folder to see the source code for the examples in the running application, unless you export a release build:
C:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0\samples\explorer\charts
C:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0\samples\explorer\containers
C:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0\samples\explorer\controls
C:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0\samples\explorer\core
C:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0\samples\explorer\effects
C:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0\samples\explorer\formatters
C:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0\samples\explorer\print
C:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0\samples\explorer\states
C:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0\samples\explorer\validators