I carry a company-supplied Dell X300 Latitude. It's the perfect size and I hardly notice it in my briefcase. It's several years old and hasn't given me much trouble. I did have a hard-drive failure about halfway through it's life, but I.T. was able to easily recover all my info and replace it in just a couple days.

It's basically my office on the road. Not sure what I'd do without it. Things would take days longer to accomplish without it.