S3Upload is a fairly simple extension (my first) that generates a HTML POST Form with all the required parameters required to upload a file from the browser directly to a bucket on Amazon S3.
It uses the existing ES3 extension to generate the parameters, including the signature and policy strings. However that extension did not generate the HTML form code, this does.
It’s very simple to use. For the instructions see the documentation on the S3Upload extension page.
If you have any suggestions for improvement, please post them here.
I hope this extension can be of use to you.