DC power is one way. As you addressed at the end of the article, the problem is that the demand for DC is not as large as it should be to bring costs of the power supply and infrastructure down. Better-efficient voltage regulators on the motherboard are also another way to help with the reduction of power requirements in the datacenter.

The Last option that I know of is to use AC, but switch to highly-efficient power supplies - particularly a PWS that is optimized for the application/workload that you are running. Today, most company's power supplies range in the 70-80% area of efficiency. It's important to get over the 85% hump and reach for 90%+. Over 3 years (for example) with 93% efficient power supplies in a blades system, I have reports that show a 1050 kW/hour savings per chassis of 10 blades per year. This translates into a savings of just over $4,700 in 3 years. Fill a row cabinets in a datacenter of blades and you have a ton (figuratively) of carbon reduction and hard $$ savings.

In 1U's it's a little bit more tricky, but here is a review of a server that is generating a lot of interest because of the innovative way it's saving power and money in the datacenter:
http://www.anandtech.com/showdoc.aspx?i=2997 (power consumption and savings is addressed on page 8).