Forbes has a commentary by Sun's CIO, Bob Worrall.

Commentary
A Green Budget Line
Bob Worrall 07.28.08, 6:00 AM ET
Bob Worrall

While the headlines are focused on nearly $5 gas and its impact on consumers, skyrocketing energy prices also are biting into information technology organizations as the costs of powering and cooling data centers reach all-time highs. In many companies, the cost to run data centers is now the second-largest expense after people. And the cost of powering data centers worldwide could grow from $18.5 billion in 2005 to $250 billion by 2012. There is no better time than right now to focus investment on more energy-efficient data centers.
Making the data center greener has been a hard sell. Most decision makers find the goal of reducing carbon emissions laudable but are held back by concerns that it will cut into profits or performance. When energy costs were relatively low, arguing that a current investment would reduce future costs was an uphill battle. But today's environment might provide the harsh dollars-and-cents context that's needed to move this issue from a decision about being green to one about being fiscally responsible.

Bob makes good tips in the rest of the article.

Check the vintage of the systems in your server racks, and replace energy and space hogs. Unlike fine wine, computer hardware rarely ages gracefully. Rooting out old systems is often the easiest way to make a data center more efficient. Old hardware almost always consumes more space and power than new systems. Older systems are also usually more difficult to cool efficiently. Switching to more modern systems often allows for impressive consolidation ratios ranging from 2:1 to 10:1. You gain space and save energy even as you increase your computing power.
Tie IT decision makers to their facilities counterparts. Regardless of how much electricity is being consumed by the data center, chief information officers aren't usually the ones writing the utility checks. This disconnect often fuels an unnecessary debate about the importance of compute power over cost savings. IT and facilities organizations need to collaborate to make sure both understand how energy-efficient computing will help address both. If you take the improved energy efficiency, the reduced space utilization and the rebates on servers offered by many municipal power providers, the cost to go green begins to approach negligible.
Look at virtualization and container technologies. Using the right container technologies as part of your virtualization approach isolates applications and services by using flexible, software-defined boundaries. Taking this direction can allow you to achieve even greater compression in both servers and storage. For example, one customer I worked with implemented a new storage system with built-in virtualization and eliminated 40 terabytes of physical capacity, reducing storage power and cooling costs by 60%.
Turn on the meter at the rack level. Legacy measurement of watts per square foot in a data center may show the room is running fine on average, but in reality you have hot spots throughout that are damaging equipment. Most data centers measure load at the perimeter of the data center, which predictably makes things unpredictable. It is important to take metering one step further. It needs to be measured at the rack level (watts per rack) to truly enable energy efficiency. This enables you to reduce power consumption by pinpointing attention on certain areas in a data center instead of using the traditional, scattershot approach of cranking up the fans when a particular area in the data center starts to run hot.

Note: Container Technologies mentioned are the type in this Sun White Paper for software containers, not the containers for data center equipment.