A small PSA that I missed in the run up to Christmas - Amazon's EC2 Container Registry is now available. This is a boon if you've got a bunch of small containers that you want to put in a private registry and nowhere else to do so.
(For a small number of large containers you're probably better off with the per-registry cost model of Docker Hub, rather than Amazon's storage-and-bandwidth setup)
It's a bit tricky to find at the moment. The "Get Started" guide has some links:
Otherwise you'll find a new "Repositories" tab in ECS under the us-east-1 region only.