As others have said, I would check out CloudFoundry. It is open-source & extensible.
I do exactly what you describe on a VPS in the cloud. I host my own prototype projects on a CloudFoundry instance. So far I've deployed these types of projects: Rails, Grails (JVM + Servlet), node.js, and Clojure(script). I also run production apps on CloudFoundry.
Setting up the instance(s) is easy, as there are plugins for most web frameworks already out there. I'm doing a session at Uberconf where I walk through my usage, process, and scripts for CloudFoundry. If there's enough interest, I could be convinced to screencast it.
PS: I do not work for CloudFoundry. Just a happy user.
