The research being done at IBM into cooling stacked or 3-D chips is focusing on water.  They have managed to pipe water into cooling structures as thin as a human hair (50 microns) between the individual chip layers.  They are getting some impressive results, which you can read about over at [H]ard|OCP.
 

“IBM Researchers, in collaboration with the Fraunhofer Institute in Berlin, demonstrated a prototype that integrates the cooling system into the 3-D chips by piping water directly between each layer in the stack.

These so-called 3-D chip stacks – which take chips and memory devices that traditionally sit side-by-side on a silicon wafer and stacks them together on top of one another — presents one of the most promising approaches to enhancing chip performance beyond its predicted limits.”

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