Are there any good sites that discuss the power requirements of CPUs and/or motherboaards (short of going to the manufacturer's site for specs)?

nm, found a good one . When in doubt, google is your friend .

http://www.plasma-online.de/textual/alm ... power.html

And as the document you linked shows , Via eden mini-itx is the KING of low power

I have 5 systems at my home , 4 are mini-itx and one is a dell laptop. Combined , they use less than a typical P4 box.

Here is a good pdf on the Via Eden line , very detailed break down of power usage and comparison to stanard P3 boxes

http://www.solar-guppy.com/downloads/via_power.pdf

Thanks for the document, that is great!

A question here is, if I purchase one of those DC-DC snap in modules, what type of power supply do I need to power it? One of the external "floor warts" (as opposed to wall warts) that I see listed at most of the sites that sell mini-itx boards?

Like these?
A kit: http://www.essencompu.com/nupplysingar.asp?ID=6473
another one: http://www.essencompu.com/nupplysingar.asp?ID=6474

You don't have to use those custom supplys ... there are MANY suppliers of cases , they come with the ATX supply built in and run off an external 12volt power brick

http://www.axiontech.com/prdt.php?src=PW&item=34633

or goto

http://www.pricewatch.com/

use mini-itx as the search word and have fun finding to best price

Right, but the "power brick" is the part that kind of confused me. I still need one of those to plug into that case, right (not trying to be dense here, just thorough ). Thanks again .

The power brick is a 120 vac to 12 vdc switcher , about 50 watts. These come with the case

The Case has an internal switcher that takes the 12 vdc and makes all the internal ATX voltages

the mini-itx cases come with everything to power a min-itx board , the via doc references are for make your on case types (like for car PC's)