AWS S3 Bucket - File Explorer Field
You want to have a read only access for your users, correct?
It's not so difficult to implement in Amazon S3.

First of all, you need to set up an IAM user and apply read only permissions for it. AWS provides pre-defined policy template. More information here:
http://docs.aws.amazon.com/IAM/

Once you created a user, you can connect to your storage using tools such as CloudBerry Explorer. When you client authanticats using key pairs assigned to the read only user you created, they will be able only to download files.
You can download CloudBerry Explroer here:
http://www.cloudberrylab.com/free-amazon-s3-explorer-cloudfront-IAM.aspx

Regards,
Vlad,
CloudBerry Lab