Maybe you could be more specific about your requirements, namely, electric power, size, weight, and computational power. There's a big difference between steering toward a gps waypoint and computing stereo disparity at 60fps while updating a SLAM model.
For CPUs, I'd go with a Mini-ITX Pentium-M (btw, centrino is pure marketing swill) if you're power constrained or an ATX single or dual Athlon64 if you're not. Max out the ram. Mount the hard disk (ideally mirrored, if only via ata raid) on a well engineered contraption involving springs and foam rubber.
I would advise against notebooks. You won't get the expandability you need. No PCI slots, few ports, etc. The screen and keyboard may be nice, but you're going to have to be able to do *everything* over a radio link anyway, so really they're just a waste. It will be more difficult to give the hard disk the protection it needs. The battery isn't really useful because you are going to have main battery packs large enough to run the computer anyway, and you'd probably prefer having a relatively constant load on those rather than a huge spike when the laptop decides to charge it's own batteries.
As another random thought, how about the guts out of a new mac mini? That's a dual core pentium m in a pretty small form factor.
chris