I have been looking for a suitable solution for a small field server/PC to run Linux and support basic needs. I was most interested in the 12V DC requirement for use with solar systems. I finally got around to building one from a bare bones kit from http://www.mini-box.com/ - As with most electronics there are several sites that sell this kind of equipment, but I went with mini-box because they have a good selection of 12V DC power supplies.

The one I built is the basic VoomPC, which is actually marketed as a carputer. The case is a nice piece of aluminum with built in heat fins and a single case fan. I had hoped to go with with a fanless system, but ended up getting the basic Intel motherboard to keep costs/power down. Here are the specs:

-Intel D945GCLF2 Mini-ITX Motherboard kit
-Intel Atom 1.6GHz
-2GB RAM
-4GB IDE Flash Drive
-PicoPSU 90 power supply
-10/100 Ethernet (no wireless)

The kit: http://tinyurl.com/bfmmmx

Total cost of the build with shipping was just under $280.

Notes:
-Power draw was about 24 watts. The PicoPSU is a very slick piece of gear.
-Motherboard does have a PCI slot but you would need a right angle adapter or PCI cable to use it [with this case].
-Sound level (perceptual) is higher than I thought it would be with the case and MB fan running. May not matter in a car install, but you would not want it next to you on the desk for very long.
-The fan on the MB is actually for the 945 chipset as the Atom CPU only needs a small heat sink. If Intel can upgrade this chipset the heat and power draw could be reduced. I have no idea if/when that might happen.
-This is a carputer without a car so I got an old PC reset switch from the friendly people at the local Computer Renaissance and use it as a power switch. You can get a momentary switch from Radio Shack for about 3 bucks. Or if your steady of hand just short the jumpers on the MB with a screw driver (This is where I tell you that shorting electrical stuff with a screwdriver is really dumb and could cause injury or just ruin your day in general.)
-I installed/lightly tested Ubuntu 8.10 and then Fedora 10 and they both fit (separately) on the 4GB Flash with about 2GB to spare. That also leaves the SATA ports open if you needed more drive space for data. 4GB is not enough if you want to size a swap partition that's bigger than RAM (2GB in this case). Go with the 8GB or plan to use the 4GB flash drive for only the OS and put the home/swap partitions on the second SATA drive.
-If you do not need the carputer form factor (it reminds me of an amplifier) this case might work (it's also half the price): http://tinyurl.com/cfvohp

Next Steps:
-Build/Test mini video server with minimal CentOS install and Zoneminder.
-Build/Test mini SMS server with linux and FrontlineSMS with Falcom Samba 75 as GSM modem.

Enjoy,
Coby