You can use a bucket policy to give anonymous users full read access to your objects. Depending on whether you need them to LIST or just perform a GET, you'll want to tweak this. (I.e. permissions for listing the contents of a bucket have the action set to "s3:ListBucket").
http://docs.aws.amazon.com/AmazonS3/latest/dev/AccessPolicyLanguage_UseCases_s3_a.html
Your policy will look something like the following. You can use the S3 console at http://aws.amazon.com/console to upload it.
{
"Version":"2008-10-17",
"Statement":[{
"Sid":"AddPerm",
"Effect":"Allow",
"Principal": {
"AWS": "*"
},
"Action":["s3:GetObject"],
"Resource":["arn:aws:s3:::bucket/*"
]
}
]
}
If you're truly opening up your objects to the world, you'll want to look into setting up CloudWatch rules on your billing so you can shut off permissions to your objects if they become too popular.