GigaOm has a post on 4 data center tools for energy efficient data centers, focusing on server power management.
Appistry EnergySaver: An add-on to Appistry’s Enterprise Application Fabric, EnergySaver lets customers define performance-based policies for power management. When resources are no longer necessary, EnergySaver puts them to sleep, only bringing them back up as needed. If target resource utilization for a system is set at 50 percent, EnergySaver can power on or power off machines to keep aggregate usage at the predefined level.
Cassatt Active Power Management: Available across Cassatt’s line of Active Response solutions or as a standalone product, Active Power Management takes into account a variety of factors — from system performance to your electric utility’s peak and off-peak pricing schedules — to determine when to turn servers on and off. If machines are needed for failover or to maintain application service levels, Active Power Management can bring them back up automatically.
Virtual Iron LivePower: A standard but still “experimental” feature of Virtual Iron v4.4, LivePower lets users set pre-determined utilization levels for physical machines. (Virtual Iron calls the feature experimental because “it has not yet been widely tested in production environments.”) When utilization falls below that level, LivePower leverages Virtual Iron LiveCapacity to move VMs running on that machine elsewhere. The physical server is shut down, rebooting and reentering the pool as demand picks up.
VMware Distributed Power Management: Another “experimental” feature, Distributed Power Management (DPM) is part of VMware Distributed Resource Scheduler (DRS). DPM monitors power consumption in DRS pools and uses vMotion to consolidate workloads onto fewer physical servers automatically. Unneeded physical machines go into standby mode and come back online as predefined utilization policies dictate.