Amazon EC2
See also the Cloud images dedicated page.
Comparison of stacks
ImageFactory
Steve Loranz wrote, in September 2012, on the Cloud SIG mailing list: "Just a quick note on the difference between ImageFactory and Oz.
Oz creates a KVM image, does a Just Enough OS (JEOS) install of the operating system, and provides a means to adding additional packages to and/or running customization scripts on the OS installed in this image.
ImageFactory creates a base image and then performs the necessary transformations on the image file itself to allow it to be used on any number of clouds (RHEV-M, vSphere, EC2, etc). ImageFactory can then push this image up to a cloud provider/region so that it can be used for instances.
ImageFactory uses Oz to create the base image before transforming that image for use on various clouds. In version 2 of ImageFactory, we introduce a plugin API that allows one to add plugins for new operating systems and/or new cloud types. The Fedora/RHEL plugin we include with ImageFactory uses Oz to create base images for those operating systems, but one could just as easily replace that plugin with one that uses some other library/tool.
If what you are looking for is creating images that will work on multiple clouds, please have a look at ImageFactory. It offers a CLI and REST api. v2 will be officially released soon: https://github.com/aeolusproject/imagefactory
If you just want to create images for use with KVM, Oz is solid: https://github.com/clalancette/oz
-steve"