I need an Amazon S3 user with full access to a single bucket

Are you aware of the AWS Policy Generator?

You need to grant s3:ListBucket permission to the bucket itself. Try the policy below.

{
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "S3:*",
      "Resource": "arn:aws:s3:::bar/*",
      "Condition": {}
    },
    {
      "Effect": "Allow",
      "Action": [
        "s3:ListBucket"
      ],
      "Resource": "arn:aws:s3:::bar",
      "Condition": {}
    }
  ]
}

The selected answer didn't work for me, but this one did:

{
  "Statement": [
    {
      "Action": "s3:*",
      "Effect": "Allow",
      "Resource": [
        "arn:aws:s3:::my-bucket",
        "arn:aws:s3:::my-bucket/*"
      ]
    }
  ],
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "s3:ListAllMyBuckets",
      "Resource": "arn:aws:s3:::*"
    }
  ]
}

Credit: http://mikeferrier.com/2011/10/27/granting-access-to-a-single-s3-bucket-using-amazon-iam/