When I first stumbled across SWFUpload about two years ago I was impressed by how easy it was to implement. However, their example code has always bugged me as being rather crap, having to assign a separate global event handler for each event, and the lack of multiple handlers for a single event.
SWFUpload is a small JavaScript/Flash library to get the best of both worlds. It features the great upload capabilities of Flash and the accessibility and ease of HTML/CSS.