The 2.0 GHz Intel Core 2 Duo Mac mini is at the top of the chart, sipping just .94W when turned off (power still goes to circuits monitoring the power status of the computer), 1.71W when in sleep mode, and just 12.6W when turned on but in an idle mode. sust-it calculated the energy cost per year for the mini (without a monitor, of course) as US$5.51 when calculated with the average US electrical rate. It's interesting to note that this model is no longer produced by Apple, and that the new 2.26 GHz mini is even more energy efficient. Apple's own environmental report for the mini shows that the revised model uses only .80W when turned off, 1.39W in sleep mode, but 13.4W while in idle mode.
Not surprisingly, other Apple models were near the top of the charts in both the laptop and all-in-one computer categories. The 1.86 GHz MacBook Air was barely edged out of first place in the laptop category by the HP Pavilion DM3. Although the two laptops had identical annual energy costs (US$2.39), the HP model had lower sleep and off power consumption than the MBA.
In the all-in-one category, the top iMac came in 6th behind eMachines, Acer, Asus, and MSI all-in-ones. Although the sust-it site is citing an iMac model that is no longer produced, even the new iMacs would be a bit behind the list-leading eMachines EZ1601.
If the power consumption and CO2 footprint of your computer is of concern to you, the sust-it site is a good place to make comparisons. Be aware, however, that due to the fast-paced changes in the computing world, the lists may be inaccurate at any particular point in time. In addition, it doesn't appear that sust-it looks at the total lifecycle energy consumption of the computers, something that Apple provides in their environmental reports for each model. When energy consumption and CO2 production are factored from raw materials at the beginning of production to recycling of an obsolete machine, Macs may very well lead the pack in all categories.