This includes both s3cmd and the s3browser, but it would be nice to delete multiple files at once. with s3cmd I picture this as
s3cmd del s3://BUCKET/*
And with the s3browser I picture something similar to phpmyadmin where checkboxes are placed to the left of each object listed in a bucket with a check all option at the bottom and a button to delete the checked items (ideally with an "Are you sure?!" pop-up to prevent accidental deletion).