Flex is fully integrated with the general infrastructure for effects, styles, data binding.Invoke web services or request XML or other data via HTTP using a rich, built-in library of data access services. Take advantage of more advanced data management capabilities, including real-time data streaming, automated data synchronization.But most times,the most wanted feature from Flex is File Upload.Though the File IO application contains the user interface that allows a user to upload or download files using Flash Player… I’m not sure you will need,the below is mine top 3 Flex upload component.

Flex File Upload Component
You can view the file upload example.It’s very small! You can see more detail at here.

Drag and Drop Multiple File Upload
Here is the tutorials about Drag and Drop Multiple File Upload.It’s actually using Flex 3 and Adobe AIR.The server side is using the Ruby on Rails gem Merb to handle the received files.

File Upload with Apollo and JavaScript
This project showed the powerful combination of AIR and JavaScript.It is only an experiment so, it doesn’t currently support the ability to run as a background process.If you are thinking about offline/online solution for your application and in the mean time deal with files,you will need it!