This is the Celeron Wattage Listing
Keep in mind the EIOS are no longer available
http://ark.intel.com/ProductCollection. ... milyID=288
Two things to keep in mind. Unless you're running a Database app, you don't need lots of CPU for a light duty server. This means either a low power Celeron or Sempron is good enough and you don't even need to go bleeding edge since WHS does not have a 64bit version yet. Throw 3GB at it with a reasonable CPU and you should be good to go.
My suggestion is to simply forget AMD as it's almost impossible to find boards that support the Sempron. Most DIY'ers are interested in Power, not energy efficiency, which means Intel - They've got far more options and it's their chipset that supports the CPU's.
Look for something with Onboard Graphics, Network, SATA3 and support for the Celeron of your choice. You also want at least 2GB of memory though 4GB will be much better. What you're looking for will be in the M-ATX form factor with onboard video/networking and sound. Nothing fancy and in the budget end. TIP
For things that take time (video transcoding) just run them in the background on the server. You have CPU cycles to spare and once done, they're in a specific folder shared with the devices that handle that format.
Jhoffma: My desktop, Monitor, Router all on my UPS use 95 watts right now. I've not seen more then 150 watts used total by the entire system even when I was Folding - So even though you're using less then GP, you're still using to much