Would be nice to create a list and go adding so people are aware of the options. I am going to start with a few, please feel free to add what you know. (Also I might have somethings wrong, please correct me)
- ec2 (amazon)
- open nebula
- ubuntu enterprise cloud (I believe this runs on open nebula)
- Eucalypus
- rightscale ??
- SunCloud (no its not a pun )