I've used clusters in industrial and academic settings, but they were owned by the organizations I worked for. I've never purchased time from a company that sells cluster/cloud/grid time.
Suppose I want to run some compute intensive program like as a large simulation or a data mining application. Or maybe I want to optimize a complete build of a large product suite by running a distributed build on outsourced infrastructure. Where would I purchase cluster time to run such programs?
I'm interested in learning about clusters that run popular OS platforms like Linux, BSD, Mac OS X, and Windows.
Obviously, there is the build-your-own-cluster solution using the fast, cheap hardware available these days, but I'm specifically interested in an outsourced solution.
You might want to check out Amazon's EC2 service:
Some people have already done some work in regards to clustering with EC2:
Additionally, Microsoft has offered Windows Azure, which has native hooks for .NET, allows you to run anything, really (Java, php), given that you are able to load a runtime and code from storage (or deployed with your app, but that has it's own set of pros/cons).