Layout-o-matic from InkNoise creates a CSS layout. The Layout-o-matic will generate several CSS layouts, using either pixels or percentages (nothing with ems yet).
InkNoise has another tool called “The Amazing Rolloverer” that generates Javascript-free, accessible menubars using your own images.
InkNoise’s main business is a personal Web publishing tool. I don’t know how long this free tool will be online here, as it is in a directory on the InkNoise site called experimental, but if it moves into the main realm of this site you can probably find it again.