In the forefront is Google's participation in the Climate Savers Computing Initiative, which "brings together industry, consumers and conservation organizations to significantly increase the energy efficiency of computers and servers."

For its own use, the company is building a large server farm in the The Dalles of Oregon, citing the region's renewable energy (hydroelectric) and temperate climate (reduced cooling). Waste heat is reported to be further addressed by evaporative cooling, using water pumped through the data center from the Columbia River.

Google is also working with computer manufactures to build servers that only require 12V DC power, an approach more energy-efficient than the current practice of each unit requiring 120V AC and then converting it to DC internally.

Update 2009.02.18
Google has made significant advancements in sustainable data centers and has posted detailed reports at http://www.google.com/corporate/green/datacenters/

Update 2009.09.14
The Columbia River Basin has become home to large data centers for Microsoft, Yahoo, Amazon, Ask, Intuit, and even the National Security Agency. More about mega data centers.

One criticism of the popularity of the Columbia River Basin is that while massive hydroelectric projects like these do yield energy with a low carbon footprint, other environmental impacts make the energy arguably not so 'green'. Another is that these companies are benefiting from large energy consumption subsidized by taxpayers at prices well below the US average.