Arnold renderer is an impressive renderer currently in development by a company called Solid Angle. Though it's still in a closed beta, Rudy Cortez is already working on an exporter for blender called BtoA. He originally started on it back in 2.49, but paused to wait for the new 2.5 api to be finished before going ahead with it again. Hopefully when Arnold is available to the public there'll be a blender exporter on it's way too!
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