Is there cloud software like Eucalyptus that will let you easily 'flip a switch' and start expanding onto EC2 as additional 'virtual' Eucalyptus(or whatever) nodes?
Thats exactly what Eucalyptus is for isn't it? Are you asking for an alternative to Eucalyptus?
I don't know the details of Eucalpytus, but it sounds like you are talking about Platform-As-A-Service (PaaS), where you pay to put your application on a cloud platform, and can then expand it as needed.
I would like to amend an answer made previously: RightScale is not a PaaS management tool. It is a cloud management software on top of public or private IaaS. However, cloud management software can indeed manage multiple cloud at the same time (Eucalyptus and Amazon EC2 for example). RightScale is one of them, but you can have a look at enStratus or Scalr (disclaimer: I work there).
If you really look for PaaS, you should check out Heroku and Cloud Foundry.
Thats exactly what Eucalyptus is for isn't it? Are you asking for an alternative to Eucalyptus?
I don't know the details of Eucalpytus, but it sounds like you are talking about Platform-As-A-Service (PaaS), where you pay to put your application on a cloud platform, and can then expand it as needed.
Apart from EC2, other PaaS platforms include Force.com and SaaSGrid
Turns out what I'm actually looking for is more of a PaaS managment tool. RightScale seems to be what I need, I think.
VMware vSphere allows grabbing resources from external clouds. Their Appspeed product looks like it will do it based on an application SLA.
I would like to amend an answer made previously: RightScale is not a PaaS management tool. It is a cloud management software on top of public or private IaaS. However, cloud management software can indeed manage multiple cloud at the same time (Eucalyptus and Amazon EC2 for example). RightScale is one of them, but you can have a look at enStratus or Scalr (disclaimer: I work there).
If you really look for PaaS, you should check out Heroku and Cloud Foundry.