The only problem with those super-slim notebooks (and I had one of the old Sony ultra-slim models) is they don't have a CD drive, so by the time you start lugging around an external CD drive, and the power cords and everything else, it's not much smaller than a regular notebook.

Dell makes what is probably the largest laptop, the M2010. It has a 20 inch screen and weighs over 18 pounds! It's a return to the age of the luggable computer, along the lines of the Osborne or Kaypro.