Intel's newer low-power Xeons are making their way into servers, and IBM now has added several new servers to their System X line. They've also added several servers with AMD Opterons in them as well, relying on the low-power "HE" and "EE" low-power models. AMD's "EE" model Opteron reigns in as the king for power consumption, operating at 1.8GHz and requiring 40W of power, along with being coupled to DDR2 modules that use less power than comparable Intel FB-DIMMs. Intel's offerings are using the Clovertown core that has gotten so much good press, and both require 50W at 1.6GHz and 1.86GHz. AMD's "HE" model takes a little more, at 65W, but operates at 2.6GHz.
Over time, the reduction in power consumption adds up considerably - especially in environments where dozens of servers are required. Even though at the enthusiast end our power demands seem to be going up and up, there are leaps and bounds being made for power demands in the enterprise sector. Hopefully, many of these technologies won't be so obscenely expensive in the near future.