FancyUpload is a file-input replacement tool that features an unobtrusive multiple-file selection menu and queued upload, with an animated progress bar. It is easy to set up, server-independent and completely styleable via CSS and XHTML. It uses MooTools, so it works in all modern browsers. Check out the demo here.
The Extension:UploadForm is an Ext.form.BasicForm extension that allows you to easily upload multiple files to a server. The files are added to a queue first and then uploaded to the server. Check out the demo here.