While doing the research for tomorrow's UploadWizard refactoring meeting, I ran into those JS libraries that seem very promising:

https://github.com/blueimp/jQuery-File-Upload Demo: http://blueimp.github.io/jQuery-File-Upload/
https://github.com/Widen/fine-uploader Demos: http://fineuploader.com/demos.html

They are both very actively maintained and cover a lot of the core upload functionality needed in UploadWizard.

I think we should review those in detail, as they might be very interesting options for UploadWizard.