There's a project at Microsoft called Dryad. Here's a good podcast with more info:
http://www.dotnetrocks.com/default.aspx?showNum=378
It uses LINQ and is supposed to be easy to use. Microsoft has it doing some production stuff for Microsoft's AdCenter.
Here's the research page.
http://research.microsoft.com/research/sv/Dryad/
Dryad is quite expressive. It completely subsumes other computation frameworks, such as Google's map-reduce, or the relational algebra. Moreover, Dryad handles job creation and management, resource management, job monitoring and visualization, fault tolerance, re-execution, scheduling, and accounting.
P.S. I don't see a download, but if you contact them and you are serious you could probably get it.
Update: it's now available for download here:
http://research.microsoft.com/en-us/downloads/03960cab-bb92-4c5c-be23-ce51aee0792c/default.aspx
