Power Reduction Quick Wins

Can you suggest any quick wins to reduce power consumption across the IT estate?

For organisations looking for quick wins to reduce power consumption across their IT estate, there are a number of options being successfully implemented by other users.  These include consolidating and virtualising as many servers as possible, perhaps using VMware; adopting company policies that state that clients should not be left logged on overnight, or which apply appropriate settings (though not necessarily through group policies, so allowing users some flexibility); using devices that reduce the voltage in the server room; purchasing lower specification equipment including low power PCs and laptops; or utilising the power benefits of Windows 7.