This little FitPC4 I've put together is a pretty impressive device. It sports a quad core processor, 16 GB of DDR3 RAM, and a Kingston DC450R 3.84TB SSD.
It's passively cooled and accepts a broad input voltage (10-15, iirc, easily powered from a battery or car cigarette lighter) and runs on no more than 25 Watts. It has dual Ethernet ports, WiFi, and plenty of USB, display and other IO available.
I have this one set up to provide non-Internet dependent maps, forward and reverse address look up for all of North America, and (soon) near-instant route planning for Southern California.
Special thanks to Sherri @ Kingston for the support - Serving map tiles, geolocation data and routing information takes a LOT of storage, but the Kingston DC450R 3.84TB drive (designed for datacenter use) is making short work of it, and enabling a broader area to be covered than I had initially planned on such a small device.