GumStix' NetStix Linux computer claims to be almost the same size as a stick of gum, but is it? Well, it's close. We wouldn't recommend putting it in your mouth, but you can use it in testing your network on the go. And it definitely fits in your pocket.
At bout 1 inch by 5 inches, you're floored at the thought of this little PC chomping away at bits in your pocket, aren't you? Their 400xm-cf is a french fry-size computer capable of connecting to a network and letting network admins test and diagnose to their hearts content.