I recently wrote about how the Flickr Uploadr tool sucks, but the other part of that article was how the web upload tools for Flickr is very nice!
FancyUpload is a set of code using Flash/Javascript to perform out of band file uploads.
This is basically how Flickr allows you to queue files for upload in their web client, and it is very useful in this sense because it would be extremely painful to be forced to post every single image individually.
For me, I am more interested in the ability to post very large files without leaving the brower in a fashion that seems to make it look like it is “stuck” when really it is just uploading a giant file.