Automator action to upload a file/folder
You can combine Automator's Run Shell Script step with the command line tool curl.

curl can upload files using the -F flag followed by a file path. See ariejan de vroom's uploading files with Curl for an example.

Your shell script can be passed a list of files from earlier Automator steps:

for f in "$@"
do
    curl -i -F "$f" http://example.org/upload
done