Maybe this is old news to some of you, if so I apologize, but I just stumbled across this.
Plupload, by the developers of the popular html text editor TinyMCE, allows you to upload files using HTML5 Gears, Silverlight, Flash, BrowserPlus or normal forms, providing some unique features such as upload progress, image resizing and chunked uploads.
If you use it, let me know what you think. The site/feature list definitely looks promising.