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)
1. ec2 (amazon)
2. open nebula
3. ubuntu enterprise cloud (I believe this runs on open nebula)
4. Eucalypus
5. rightscale ??
6. SunCloud (no its not a pun
)