Canonical's Rick Clark has announced today that the server build of Ubuntu is now available through Amazon's EC2 cloud computing service. Canonical has optimized a build of the Ubuntu Server edition for the EC2 environment and it's currently in a open beta program. Using Ubuntu in Amazon's cloud computing service is free, except for the normal costs incurred when using Amazon Web Services.
This announcement was made on the ubuntu-devel mailing list
and additional details can be found on the Ubuntu EC2 web-site