Pardon the 'cloud' buzzword.
What if you want to have your own internal Amazon or internal Rackspace? :) OpenStack (
http://www.openstack.com) fits the bill. But the catch is, you deploy the pieces. It's like having the Linux kernel plus the GNU tool chain without the other productivity and userspace apps :).
Enter the new player StackOps (
http://www.stackops.com), an OpenStack 'distribution' that comes complete with tools in an ISO :). It's is a ready-to-install cloud infrastructure (think Fedora, Ubuntu, Suse, etc..).
Enjoy!