I'm looking at having to transfer a lot of large files from a 3rd party system to a cloud based file storage system, such as Rackspace Cloudfiles or Amazon S3. I'm not limited to just using those two, however.
What I'm trying to find is a way to just let those services download the files directly, once provided with a public URL, in order to speed up the transfer and avoid having to setup something in the middle that relays each file.
Is there a service out there that has an option like this available via an API or a file list upload?
All modem cloud (object) storage service meet your requirement, I think. For exmaple, AWS S3, supports set canned ACL to public when putting object (uploading file).
http://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPUT.html