You can now run SQL Server Enterprise Edition as a License Included offering on Amazon RDS. The License Included offering for the Enterprise Edition is available on R3.2xlarge, R3.4xlarge, and R3.8xlarge instance types, in the US-East (Virginia), US-West (Oregon) and Europe (Ireland) regions. In the License Included service model, you do not need separately purchased Microsoft SQL Server licenses. License Included pricing is inclusive of software license, underlying hardware resources, and Amazon RDS management capabilities. This allows you to pay for the hours you use and change your instance type as needed to fit your workloads.

Source: Amazon Web Services News