UPDATE: This is now available as a free ASP.NET control.
Recently, Joe Stagner created some videos and talked about 4 upload scenarios that provide an AJAX-like file upload experience. I've used or looked at all of those options at least once or twice in the past, but they were never quite what I wanted. I wanted something sleek and sexy. Something that really popped. The file upload tool that is my new best friend is SWFUpload.